ILLINOIS POWER CO
SC 13E4, 1998-03-03
ELECTRIC & OTHER SERVICES COMBINED
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<PAGE>   1
 
- --------------------------------------------------------------------------------
 
                       SECURITIES AND EXCHANGE COMMISSION
                             WASHINGTON, D.C. 20549
                               ------------------
 
                         Issuer Tender Offer Statement
     (Pursuant to Section 13(e)(1) of the Securities Exchange Act of 1934)
 
                             ILLINOIS POWER COMPANY
                                (Name of Issuer)
 
                              ILLINOVA CORPORATION
                       (Name of Person Filing Statement)
 
                               ------------------
 
<TABLE>
<CAPTION>
                       TITLE                                           CUSIP NUMBER
                       -----                                           ------------
<S>                                                 <C>
    CUMULATIVE PREFERRED STOCK ($50 PAR VALUE)
                   4.08% SERIES                                         452092 20 8
                   4.20% SERIES                                         452092 30 7
                   4.26% SERIES                                         452092 40 6
                   4.42% SERIES                                         452092 50 5
                   4.70% SERIES                                         452092 60 4
                   7.75% SERIES                                         452092 79 4
                            (Title and CUSIP Number of Class of Securities)
</TABLE>
 
                          LEAH MANNING STETZNER, ESQ.
                    GENERAL COUNSEL AND CORPORATE SECRETARY
                              ILLINOVA CORPORATION
                               500 S. 27TH STREET
                               DECATUR, IL 62525
                                 (217) 424-6600
 
                                with a copy to:
 
                             ROBERT J. REGAN, ESQ.
                             SCHIFF HARDIN & WAITE
                                7200 SEARS TOWER
                            CHICAGO, ILLINOIS 60616
                                 (312) 258-5606
 
  (Name, Address and Telephone Number of Person Authorized to Receive Notices
          and Communications on Behalf of the Person Filing Statement)
 
                               ------------------
 
                              ON OR ABOUT   , 1998
     (Date Tender Offer First Published, Sent or Given to Security Holders)
 
                               ------------------
 
                           CALCULATION OF FILING FEE
- --------------------------------------------------------------------------------
TRANSACTION VALUATION*  $52,607,718.80          AMOUNT OF FILING FEE  $10,521.54
- --------------------------------------------------------------------------------
* Solely for purposes of calculating the filing fee and computed pursuant to
  Section 13(e)(3) of the Securities Exchange Act of 1934, as amended, and Rule
  0-11(b)(1) thereunder, the transaction value equals the total amount of funds,
  excluding fees and other expenses, required to purchase all outstanding shares
  of each class of securities listed above pursuant to the Offer described in
  the Offer to Purchase and Proxy Statement filed as Exhibit 99(a)(1) hereto.
  The purchase price per share for the outstanding shares will be based on a
  formula utilizing the 30-year Treasury Bond rate (except that the 5-year
  Treasury Bond rate will be used with respect to the 7.75% Series) at the
  commencement of the Offer. The above transaction value is based on the formula
  utilizing the 30-year and 5-year Treasury Bond rates as of February 25, 1998.
  Any adjustments to the filing fee will be made upon filing an Amendment to
  this Schedule 13E-4 upon commencement of the Offer.
 
  [ ] Check box if any part of the fee is offset as provided by Rule 0-11(a)(2)
      and identify the filing with which the offsetting fee was previously paid.
      Identify the previous filing by registration statement number, or the form
      or schedule and the date of its filing.
 
Amount Previously Paid: ____________________     Filing Party:
 
Form or Registration No.:      Date Filed:
- --------------------------------------------------------------------------------
<PAGE>   2
 
ITEM 1. SECURITY AND ISSUER.
 
     (a) Incorporated herein by reference to the information appearing on the
front cover of the Offer to Purchase and Proxy Statement, dated                ,
1998, filed as Exhibit 99(a)(1) to this Issuer Tender Offer Statement on
Schedule 13E-4 (the "Offer to Purchase and Proxy Statement").
 
     (b) Incorporated herein by reference to the information appearing on the
front cover of the Offer to Purchase and Proxy Statement, and to the information
appearing under the captions "Terms of the Offer -- Number of Shares; Purchase
Prices; Expiration Date; Dividends" and "Transactions and Agreements Concerning
the Shares" in the Offer to Purchase and Proxy Statement.
 
     (c) Incorporated herein by reference to the information appearing under the
caption "Price Range of Shares; Dividends" in the Offer to Purchase and Proxy
Statement.
 
     (d) Illinova Corporation, an Illinois corporation ("ILN"), is the person
filing this statement and is the parent holding company of the Issuer, Illinois
Power Company ("IPC"). ILN's principal office is at 500 S. 27th Street, Decatur,
IL 62525.
 
ITEM 2. SOURCE AND AMOUNT OF FUNDS OR OTHER CONSIDERATION.
 
     (a) Incorporated herein by reference to the information appearing under the
caption "Source and Amount of Funds" in the Offer to Purchase and Proxy
Statement.
 
     (b) Incorporated herein by reference to the information appearing under the
caption "Source and Amount of Funds" in the Offer to Purchase and Proxy
Statement.
 
ITEM 3. PURPOSE OF THE TENDER OFFER AND PLANS OR PROPOSALS OF THE ISSUER OR
AFFILIATE.
 
     Incorporated herein by reference to the information appearing under the
captions "Special Factors -- Purpose of the Offer; Certain Effects of the Offer;
Plans of ILN and IPC After the Offer" and "Proposed Amendment and Proxy
Solicitation -- Reasons for the Proposed Amendment" in the Offer to Purchase and
Proxy Statement.
 
ITEM 4. INTEREST IN SECURITIES OF THE ISSUER.
 
     Incorporated herein by reference to the information appearing under the
caption "Transactions and Agreements Concerning the Shares" in the Offer to
Purchase and Proxy Statement.
 
ITEM 5. CONTRACTS, ARRANGEMENTS, UNDERSTANDINGS OR RELATIONSHIPS WITH RESPECT TO
        THE ISSUER'S SECURITIES.
 
     Incorporated herein by reference to the information appearing under the
caption "Transactions and Agreements Concerning the Shares" in the Offer to
Purchase and Proxy Statement.
 
ITEM 6. PERSONS RETAINED, EMPLOYED OR TO BE COMPENSATED.
 
     Incorporated herein by reference to the information appearing under the
caption "Fees and Expenses Associated with the Offer" in the Offer to Purchase
and Proxy Statement.
 
ITEM 7. FINANCIAL INFORMATION.
 
     (a) Incorporated herein by reference to IPC's financial statements included
in the Annual Report on Form 10-K for the year ended December 31, 1997 (to be
filed by IPC by March 10, 1998), referenced herein as Exhibit 99(g)(1) and to
the information appearing under the caption "Summary of Consolidated Financial
Information" in the Offer to Purchase and Proxy Statement.
 
     (b) Not applicable.
 
                                        2
<PAGE>   3
 
ITEM 8. ADDITIONAL INFORMATION.
 
     (a) Not applicable.
 
     (b) Incorporated herein by reference to the information appearing under the
caption "Special Factors -- Certain Legal Matters; Regulatory Approvals;
Dissenters' Rights" and "Terms of the Offer -- Certain Conditions of the Offer"
in the Offer to Purchase and Proxy Statement.
 
     (c) Not applicable.
 
     (d) Not applicable.
 
     (e) See Exhibits 99(a)(1) and 99(a)(2).
 
ITEM 9. MATERIAL TO BE FILED AS EXHIBITS.
 
<TABLE>
<CAPTION>
    EXHIBIT NO.                            DESCRIPTION
    -----------                            -----------
    <S>            <C>
    99(a)(1)       Offer to Purchase and Proxy Statement, dated             ,
                   1998.
    99(a)(2)       Form of Letter of Transmittal and Proxy.
    99(a)(3)       Form of Separate Proxy.
    99(a)(4)       Form of Notice of Guaranteed Delivery.
    99(a)(5)       Notice of Special Meeting of Shareholders.
    99(a)(6)       Form of Letter to Brokers, Dealers, Commercial Banks, Trust
                   Companies and Other Nominees.
    99(a)(7)       Form of Letter to Clients of Brokers, Dealers, Commercial
                   Banks, Trust Companies and Other Nominees.
    99(a)(8)       Letter to Shareholders, dated             , 1998.
    99(a)(9)       Summary Advertisement, dated             , 1998.*
    99(a)(10)      Press Release, dated             , 1998*
    99(b)          Credit Agreement, dated as of June 12, 1996, as amended on
                   June 28, 1996, among ILN, CIBC Inc., as Administrative
                   Agent, The First National Bank of Chicago, Bank of America
                   Illinois, The First National Bank of Boston, Bank of
                   Montreal, The Fuji Bank, Limited, ABN AMRO Bank N.V. Chicago
                   Branch, The Bank of New York and Deutsche Bank A.G. New York
                   Branch and/or Cayman Islands Branch.
    99(c)          Not applicable.
    99(d)          Not applicable.
    99(e)          Not applicable.
    99(f)          Not applicable.
    99(g)(1)       Annual Report on Form 10-K for the year ended December 31,
                   1997, (to be filed by IPC by March 10, 1998) incorporated by
                   reference to SEC File No. 1-3004.*
</TABLE>
 
- -------------------------
* To be filed by amendment.
 
                                        3
<PAGE>   4
 
                                   SIGNATURE
 
     After due inquiry and to the best of my knowledge and belief, I certify
that the information set forth in this statement is true, complete and correct.
 
Dated: March 2, 1998                      ILLINOVA CORPORATION
 
                                          By: /s/ Leah Manning Stetzner
 
                                            ------------------------------------
                                            Leah Manning Stetzner,
                                            General Counsel and Corporate
                                              Secretary
 
                                        4

<PAGE>   1
 
OFFER TO PURCHASE AND PROXY STATEMENT
 
                              ILLINOVA CORPORATION
                           OFFER TO PURCHASE FOR CASH
           ANY AND ALL OUTSTANDING SHARES OF THE FOLLOWING SERIES OF
                         CUMULATIVE PREFERRED STOCK OF
 
                             ILLINOIS POWER COMPANY
283,290 SHARES, CUMULATIVE PREFERRED STOCK, 4.08% SERIES AT A PURCHASE PRICE OF
                     $  PER SHARE, CUSIP NUMBER 452092 20 8
167,720 SHARES, CUMULATIVE PREFERRED STOCK, 4.20% SERIES AT A PURCHASE PRICE OF
                     $  PER SHARE, CUSIP NUMBER 452092 30 7
136,000 SHARES, CUMULATIVE PREFERRED STOCK, 4.26% SERIES AT A PURCHASE PRICE OF
                     $  PER SHARE, CUSIP NUMBER 452092 40 6
134,400 SHARES, CUMULATIVE PREFERRED STOCK, 4.42% SERIES AT A PURCHASE PRICE OF
                     $  PER SHARE, CUSIP NUMBER 452092 50 5
176,000 SHARES, CUMULATIVE PREFERRED STOCK, 4.70% SERIES AT A PURCHASE PRICE OF
                     $  PER SHARE, CUSIP NUMBER 452092 60 4
241,700 SHARES, CUMULATIVE PREFERRED STOCK, 7.75% SERIES AT A PURCHASE PRICE OF
                     $  PER SHARE, CUSIP NUMBER 452092 79 4
                     -------------------------------------
 
                             ILLINOIS POWER COMPANY
                                PROXY STATEMENT
        WITH RESPECT TO ITS COMMON STOCK AND CUMULATIVE PREFERRED STOCK
                     -------------------------------------
 
     THE OFFER AND WITHDRAWAL RIGHTS WILL EXPIRE AT 5:00 P.M., NEW YORK CITY
TIME, ON [EXPIRATION DATE], UNLESS THE OFFER IS EXTENDED (THE "EXPIRATION
DATE").
    Illinova Corporation, an Illinois corporation ("ILN"), invites the holders
of each series of cumulative preferred stock (par value $50 per share) listed
above (each a "Series of Preferred," and the holder thereof a "Preferred
Shareholder") of Illinois Power Company, an Illinois corporation and direct
utility subsidiary of ILN ("IPC"), to tender any and all of their shares of a
Series of Preferred ("Shares") for purchase at the purchase price per Share
listed above (the "Purchase Price"), net to the seller in cash, upon the terms
and subject to the conditions set forth in this Offer to Purchase and Proxy
Statement and in the accompanying Letter of Transmittal and Proxy (which
together constitute the "Offer"). ILN will purchase any and all Shares validly
tendered and not withdrawn, upon the terms and subject to the conditions of the
Offer. See "Terms of the Offer -- Certain Conditions of the Offer" and "Terms of
the Offer -- Extension of Tender Period; Termination; Amendments."
    THE OFFER FOR A SERIES OF PREFERRED IS NOT CONDITIONED UPON ANY MINIMUM
NUMBER OF SHARES OF SUCH SERIES OF PREFERRED BEING TENDERED AND IS INDEPENDENT
OF THE OFFER FOR ANY OTHER SERIES OF PREFERRED. THE OFFER, HOWEVER, IS
CONDITIONED UPON, AMONG OTHER THINGS, THE PROPOSED AMENDMENT, AS DESCRIBED
BELOW, BEING ADOPTED AT THE SPECIAL MEETING (AS DEFINED BELOW). SEE "TERMS OF
THE OFFER -- CERTAIN CONDITIONS OF THE OFFER."
    Concurrently with the Offer, the Board of Directors of IPC is soliciting
proxies for use at a special meeting of shareholders of IPC to be held at IPC's
principal office, 500 South 27th Street, Decatur, Illinois 62525, on [EXPIRATION
DATE] at 4:30 p.m., New York City time, or any adjournment or postponement of
such meeting (the "Special Meeting"). The purpose of the Special Meeting is to
consider an amendment (the "Proposed Amendment") to IPC's Amended and Restated
Articles of Incorporation (the "Articles") which would remove a provision of the
Articles that limits IPC's ability to issue or assume unsecured indebtedness
(the "Debt Limitation Provision"). WHILE PREFERRED SHAREHOLDERS WHO WISH TO
TENDER THEIR SHARES PURSUANT TO THE OFFER ARE NOT REQUIRED TO VOTE IN FAVOR OF
THE PROPOSED AMENDMENT, THE OFFER IS CONDITIONED UPON THE PROPOSED AMENDMENT
BEING ADOPTED AT THE SPECIAL MEETING. IN ADDITION, PREFERRED SHAREHOLDERS HAVE
THE RIGHT TO VOTE FOR THE PROPOSED AMENDMENT REGARDLESS OF WHETHER THEY TENDER
THEIR SHARES. IF THE PROPOSED AMENDMENT IS ADOPTED AT THE SPECIAL MEETING, IPC
WILL MAKE A SPECIAL CASH PAYMENT (AS DEFINED HEREIN) IN THE AMOUNT OF $    PER
SHARE TO EACH PREFERRED SHAREHOLDER WHO VOTED IN FAVOR OF THE PROPOSED
AMENDMENT, PROVIDED THAT SUCH SHARES HAVE NOT BEEN TENDERED PURSUANT TO THE
OFFER. THOSE PREFERRED SHAREHOLDERS WHO VALIDLY TENDER THEIR SHARES WILL BE
ENTITLED ONLY TO THE PURCHASE PRICE PER SHARE LISTED ABOVE.
                     -------------------------------------
 
    ILN will pay to a Soliciting Dealer (as defined herein) a solicitation fee
for Shares tendered, accepted for payment and paid for pursuant to the Offer,
subject to certain conditions. See "Fees and Expenses Associated with the
Offer."
                     -------------------------------------
 
    THIS TRANSACTION HAS NOT BEEN APPROVED OR DISAPPROVED BY THE SECURITIES AND
EXCHANGE COMMISSION (THE "SEC") NOR HAS THE SEC PASSED UPON THE FAIRNESS OR
MERITS OF THIS TRANSACTION NOR UPON THE ACCURACY OR ADEQUACY OF THE INFORMATION
CONTAINED IN THIS DOCUMENT. ANY REPRESENTATION TO THE CONTRARY IS UNLAWFUL.
                     -------------------------------------
 
    NEITHER ILN, IPC, THEIR RESPECTIVE BOARDS OF DIRECTORS, NOR ANY OF THEIR
RESPECTIVE OFFICERS MAKES ANY RECOMMENDATION TO ANY PREFERRED SHAREHOLDER AS TO
WHETHER TO TENDER ANY OR ALL SHARES. EACH PREFERRED SHAREHOLDER MUST MAKE HIS OR
HER OWN DECISION AS TO WHETHER TO TENDER SHARES AND, IF SO, HOW MANY SHARES TO
TENDER.
                     -------------------------------------
 
     IPC'S BOARD OF DIRECTORS RECOMMENDS VOTING FOR THE PROPOSED AMENDMENT.
                     -------------------------------------
    This Offer to Purchase and Proxy Statement is first being mailed on or about
[STATEMENT DATE] to Preferred Shareholders of record on [RECORD DATE].
    IPC has declared the regular quarterly dividend on each Series of Preferred
to be paid on May 1, 1998 (the "May 1998 Dividend") to holders of record as of
the close of business on April 9, 1998. A tender and purchase of Shares pursuant
to the Offer will not deprive a Preferred Shareholder of his or her right to
receive the May 1998 Dividend on his or her Shares held of record as of the
close of business on April 9, 1998, regardless of whether such Preferred
Shareholder tenders his or her Shares in the Offer prior to that date. Tendering
Preferred Shareholders will not be entitled to any dividends in respect of any
dividend period (or any portion thereof) after May 1, 1998.
    Each Series of Preferred is traded on the New York Stock Exchange, Inc. (the
"NYSE"), except the 7.75% Series which trades in the over-the-counter market
(the "OTC"). On [LAST SALE DATE REFERENCE], the last reported sales prices on
the NYSE were $    for the 4.08% Series of Preferred (on         ); $    for the
4.20% Series of Preferred (on       ); $    for the 4.26% Series of Preferred
(on         ); $
for the 4.42% Series of Preferred (on         ); and $    for the 4.70% Series
of Preferred (on         ). On [LAST SALE DATE REFERENCE], the last reported
sales price as reported by the National Quotation Bureau, Inc. was $    for the
7.75% Series of Preferred (on         ). Preferred Shareholders are urged to
obtain a current market quotation, if available, for their Shares.
                     -------------------------------------
                      THE DEALER MANAGER FOR THE OFFER IS:
 
                          DONALDSON, LUFKIN & JENRETTE
                             SECURITIES CORPORATION
  The date of this Offer to Purchase and Proxy Statement is [STATEMENT DATE].
<PAGE>   2
 
     NO PERSON HAS BEEN AUTHORIZED TO MAKE ANY RECOMMENDATION ON BEHALF OF ILN
OR IPC AS TO WHETHER PREFERRED SHAREHOLDERS SHOULD TENDER OR REFRAIN FROM
TENDERING SHARES OF ANY SERIES OF PREFERRED PURSUANT TO THE OFFER. NO PERSON HAS
BEEN AUTHORIZED TO GIVE ANY INFORMATION OR TO MAKE ANY REPRESENTATIONS IN
CONNECTION WITH THE OFFER OTHER THAN THOSE CONTAINED HEREIN, IN THE RELATED
LETTER OF TRANSMITTAL AND PROXY OR IN THE SEPARATE PROXY. IF GIVEN OR MADE, SUCH
RECOMMENDATION AND SUCH INFORMATION AND REPRESENTATIONS MUST NOT BE RELIED UPON
AS HAVING BEEN AUTHORIZED BY ILN OR IPC.
 
                                   IMPORTANT
 
     Any Preferred Shareholder desiring to accept the Offer and tender all or
any portion of his or her Shares should either (i) request his or her broker,
dealer, commercial bank, trust company or nominee to effect the transaction for
him or her, (ii) complete and sign the applicable Letter of Transmittal and
Proxy enclosed herewith (the "Letter of Transmittal and Proxy") in accordance
with the instructions in such Letter of Transmittal and Proxy, mail or deliver
the same and any other required documents to First Chicago Trust Company of New
York (the "Depositary"), and deliver the certificates for such Shares, together
with the Letter of Transmittal and Proxy, to the Depositary, or (iii) tender
such Shares pursuant to the procedure for book-entry transfer set forth below
under "Terms of the Offer -- Procedure for Tendering Shares," in each case on or
prior to the Expiration Date (as defined below). A Preferred Shareholder whose
Shares are registered in the name of a broker, dealer, commercial bank, trust
company or nominee must contact such broker, dealer, commercial bank, trust
company or nominee if he or she desires to tender such Shares. Any Preferred
Shareholder who desires to tender Shares and whose certificates for such Shares
are not immediately available, or who cannot comply in a timely manner with the
procedure for book-entry transfer, should tender such Shares by following the
procedures for guaranteed delivery set forth below under "Terms of the Offer --
Procedure for Tendering Shares."
 
     EACH SERIES OF PREFERRED HAS ITS OWN LETTER OF TRANSMITTAL AND PROXY AND
ITS OWN SEPARATE PROXY. ONLY THE APPLICABLE LETTER OF TRANSMITTAL AND PROXY FOR
SUCH SERIES OF PREFERRED OR A NOTICE OF GUARANTEED DELIVERY MAY BE USED TO
TENDER SHARES OF SUCH SERIES OF PREFERRED. A PROXY (WHETHER INCLUDED AS PART OF
THE LETTER OF TRANSMITTAL AND PROXY OR AS A SEPARATE DOCUMENT ENCLOSED HEREWITH)
MAY BE USED TO VOTE IN FAVOR OF THE PROPOSED AMENDMENT EVEN IF NO SHARES ARE
BEING TENDERED.
                           -------------------------
 
     Questions or requests for assistance may be directed to MacKenzie Partners,
Inc. ("MacKenzie" or the "Information Agent") or to Donaldson, Lufkin & Jenrette
Securities Corporation ("DLJ" or the "Dealer Manager") at their respective
telephone numbers and addresses set forth on the back cover of this Offer to
Purchase and Proxy Statement. Requests for additional copies of this Offer to
Purchase and Proxy Statement, the Letter of Transmittal and Proxy, the separate
Proxy or other related tender offer or proxy materials may be directed to the
Information Agent, and such copies will be furnished promptly at ILN's or IPC's
expense, as applicable. Preferred Shareholders may also contact their local
broker, dealer, commercial bank or trust company for assistance concerning the
Offer.
 
                                        2
<PAGE>   3
 
                               TABLE OF CONTENTS
 
<TABLE>
<S>                                                             <C>
SUMMARY.....................................................      4
SPECIAL FACTORS.............................................      7
  Purpose of the Offer; Certain Effects of the Offer........      7
  Liquidity of Trading Market...............................      8
  Potential Effects of the Proposed Amendment on
     Non-Tendering Preferred Shareholders...................      8
  Plans of ILN and IPC After the Offer......................      9
  Certain Legal Matters; Regulatory Approvals...............     10
  Dissenters' Rights........................................     10
TERMS OF THE OFFER..........................................     10
  Number of Shares; Purchase Prices; Expiration Date;
     Dividends..............................................     10
  Procedure for Tendering Shares............................     11
  Withdrawal Rights.........................................     13
  Acceptance of Shares for Payment and Payment of Purchase
     Price..................................................     14
  Certain Conditions of the Offer...........................     15
  Extension of Tender Period; Termination; Amendments.......     16
PROPOSED AMENDMENT AND PROXY SOLICITATION...................     17
  Introduction..............................................     17
  Voting Securities, Rights and Procedures..................     17
  Dissenters' Rights........................................     18
  Proxies...................................................     19
  Special Cash Payments.....................................     19
  Security Ownership of Certain Beneficial Owners and
     Management.............................................     20
  Business to Come Before the Special Meeting...............     21
  Explanation of the Proposed Amendment.....................     21
  Reasons for the Proposed Amendment........................     21
  Relationship with Independent Accountants.................     23
PRICE RANGE OF SHARES; DIVIDENDS............................     23
CERTAIN FEDERAL INCOME TAX CONSEQUENCES.....................     25
SOURCE AND AMOUNT OF FUNDS..................................     27
TRANSACTIONS AND AGREEMENTS CONCERNING THE SHARES...........     27
FEES AND EXPENSES ASSOCIATED WITH THE OFFER.................     27
CERTAIN INFORMATION REGARDING ILN AND IPC; INCORPORATION BY
  REFERENCE.................................................     29
SUMMARY OF CONSOLIDATED FINANCIAL INFORMATION; INCORPORATION
  BY REFERENCE..............................................     30
MISCELLANEOUS...............................................     32
ATTACHMENT A................................................    A-1
</TABLE>
 
                                        3
<PAGE>   4
 
                                    SUMMARY
 
     The following summary is provided solely for the convenience of the
Preferred Shareholders. This summary is not intended to be complete and is
qualified in its entirety by reference to the full text and more specific
details contained in this Offer to Purchase and Proxy Statement, the Letter of
Transmittal and Proxy and the separate Proxy and any amendments hereto or
thereto. Preferred Shareholders are urged to read this Offer to Purchase and
Proxy Statement, the Letter of Transmittal and Proxy and the separate Proxy in
their entirety. Each of the capitalized terms used in this summary and not
defined herein has the meaning set forth elsewhere in this Offer to Purchase and
Proxy Statement.
 
The Companies.................   Illinova Corporation ("ILN"), 500 South 27th
                                 Street, Decatur, Illinois 62525, is an exempt
                                 holding company under the Public Utility
                                 Holding Company Act of 1935, as amended (the
                                 "Holding Company Act"). ILN has three principal
                                 operating subsidiaries: Illinois Power Company
                                 ("IPC"), a combination electric and gas
                                 utility; Illinova Generating Company, an
                                 independent power supply company; and Illinova
                                 Energy Partners, Inc., an energy broker and
                                 services company. IPC is engaged in the
                                 generation, transmission, distribution and sale
                                 of electric energy and the distribution,
                                 transportation and sale of natural gas in the
                                 State of Illinois. Its service area is a widely
                                 diversified industrial and agricultural area
                                 comprising approximately 15,000 square miles in
                                 northern, central and southern Illinois.
                                 Electric service is provided at retail to 310
                                 incorporated municipalities, adjacent suburban
                                 and rural areas and numerous unincorporated
                                 municipalities. Gas service is provided to 257
                                 incorporated municipalities, adjacent suburban
                                 areas and numerous unincorporated
                                 municipalities.
 
The Shares....................   4.08% Series, Cumulative Preferred Stock (par
                                 value $50 per share)
                                 4.20% Series, Cumulative Preferred Stock (par
                                 value $50 per share)
                                 4.26% Series, Cumulative Preferred Stock (par
                                 value $50 per share)
                                 4.42% Series, Cumulative Preferred Stock (par
                                 value $50 per share)
                                 4.70% Series, Cumulative Preferred Stock (par
                                 value $50 per share)
                                 7.75% Series, Cumulative Preferred Stock (par
                                 value $50 per share)
 
The Offer and Purchase
Price.........................   Offer to purchase any or all Shares of each
                                 Series of Preferred at the prices set forth
                                 below, which prices shall be the "Purchase
                                 Price" with respect to the applicable Series of
                                 Preferred.
 
                                 $  per Share of the 4.08% Series
                                 $  per Share of the 4.20% Series
                                 $  per Share of the 4.26% Series
                                 $  per Share of the 4.42% Series
                                 $  per Share of the 4.70% Series
                                 $  per Share of the 7.75% Series
 
Independent Offer.............   The Offer for one Series of Preferred is
                                 independent of the Offer for any other Series
                                 of Preferred. The Offer is not conditioned upon
                                 any minimum number of Shares of the applicable
                                 Series of Preferred being tendered. Preferred
                                 Shareholders who wish to tender their Shares
                                 are not required to vote in favor of the
                                 Proposed Amendment. The Offer is subject,
                                 however, to adoption of the Proposed Amendment
                                 at the Special Meeting and certain other
                                 conditions described herein. See "Terms of the
                                 Offer -- Certain Conditions of the Offer."
 
                                        4
<PAGE>   5
 
Expiration Date of the
Offer.........................   The Offer expires at 5:00 p.m., New York City
                                 time on [Expiration Date], unless extended (the
                                 "Expiration Date").
 
How to Tender Shares..........   See "Terms of the Offer -- Procedure for
                                 Tendering Shares." For further information,
                                 call the Information Agent or the Dealer
                                 Manager or consult your broker for assistance.
 
Withdrawal Rights.............   Tendered Shares of any Series of Preferred may
                                 be withdrawn at any time until the Expiration
                                 Date with respect to such Series of Preferred
                                 and, unless previously accepted for payment,
                                 may also be withdrawn after
                                                     , 1998. See "Terms of the
                                 Offer -- Withdrawal Rights." Any proxy
                                 accompanying any tendered Shares that are
                                 withdrawn will not be considered revoked unless
                                 the Preferred Shareholder specifically revokes
                                 such proxy as described herein. See "Proposed
                                 Amendment and Proxy Solicitation -- Proxies."
 
Purpose of the Offer..........   ILN is making the Offer because ILN believes
                                 that the purchase of Shares is economically
                                 attractive to ILN, its shareholders and IPC. In
                                 addition, the Offer gives Preferred
                                 Shareholders the opportunity to sell their
                                 Shares at a price which ILN believes to be a
                                 premium over the current market price on the
                                 date of the announcement of the Offer and
                                 without the usual transaction costs associated
                                 with a market sale. See "Special Factors."
 
Dividends.....................   IPC has declared the regular quarterly dividend
                                 on each Series of Preferred to be paid on May
                                 1, 1998 (the "May 1998 Dividend") to holders of
                                 record as of the close of business on April 9,
                                 1998. A tender and purchase of Shares pursuant
                                 to the Offer will not deprive a Preferred
                                 Shareholder of his or her right to receive the
                                 May 1998 Dividend on his or her Shares held of
                                 record as of the close of business on April 9,
                                 1998. Tendering Preferred Shareholders will not
                                 be entitled to any dividends in respect of any
                                 dividend period (or any portion thereof) after
                                 May 1, 1998.
 
Brokerage Commissions.........   Not payable by Preferred Shareholders.
 
Solicitation Fee..............   ILN will pay a solicitation fee of
                                 $            per Share that is tendered,
                                 accepted for payment and paid for pursuant to
                                 the Offer in transactions for beneficial owners
                                 of fewer than        Shares and a solicitation
                                 fee of $            per Share for transactions
                                 for beneficial owners of        or more Shares;
                                 provided that solicitation fees payable in
                                 transactions for beneficial owners of        or
                                 more Shares shall be paid 80% to the Dealer
                                 Manager and 20% to any designated Soliciting
                                 Dealer (as defined herein) (which may be the
                                 Dealer Manager). If the Proposed Amendment is
                                 adopted at the Special Meeting, IPC will pay to
                                 each designated Soliciting Dealer a separate
                                 fee of $            per Share for Shares that
                                 are not tendered pursuant to the Offer but
                                 which are voted in favor of the Proposed
                                 Amendment in transactions for beneficial owners
                                 of fewer than        Shares and a separate fee
                                 of $            per Share for Shares that are
                                 not tendered pursuant to the Offer but which
                                 are voted in favor of the Proposed Amendment in
                                 transactions for beneficial owners of        or
                                 more Shares; provided that the separate fee
                                 payable in transactions for beneficial owners
                                 of        or more Shares shall be paid 80% to
                                 the Dealer Manager
                                        5
<PAGE>   6
 
                                 and 20% to any designated Soliciting Dealer
                                 (which may be the Dealer Manager). A Soliciting
                                 Dealer will not be entitled to a solicitation
                                 fee or a separate fee for Shares beneficially
                                 owned by such Soliciting Dealer.
 
Proposed Amendment............   Concurrently with the Offer, the Board of
                                 Directors of IPC is soliciting proxies for use
                                 at the Special Meeting. The purpose of the
                                 Special Meeting is to consider an amendment to
                                 IPC's Articles which would remove a provision
                                 that limits IPC's ability to issue or assume
                                 unsecured indebtedness. If the Proposed
                                 Amendment is adopted at the Special Meeting,
                                 the clause of the Articles that places
                                 restrictions on IPC's ability to issue or
                                 assume unsecured indebtedness will be
                                 eliminated with respect to any Shares that
                                 remain outstanding after the consummation of
                                 the Offer. See "Special Factors." Preferred
                                 Shareholders may be entitled to dissenters'
                                 rights in connection with the adoption of the
                                 Proposed Amendment. See "Proposed Amendment and
                                 Proxy Solicitation -- Dissenters' Rights."
 
Special Meeting...............   IPC will consider the Proposed Amendment at the
                                 Special Meeting to be held at its principal
                                 office, 500 South 27th Street, Decatur,
                                 Illinois 62525, on [Expiration Date] at 4:30
                                 p.m., New York City time. Only holders of
                                 record of IPC's voting securities at the close
                                 of business on the Record Date will be entitled
                                 to vote at the Special Meeting.
 
Record Date...................   [Record Date].
 
Special Cash Payment..........   If the Proposed Amendment is adopted at the
                                 Special Meeting by IPC's shareholders, IPC will
                                 make a special cash payment of $      per Share
                                 to each Preferred Shareholder who voted in
                                 favor of the Proposed Amendment but who did not
                                 tender his or her Shares (the "Special Cash
                                 Payment"). Preferred Shareholders who validly
                                 tender their Shares will be entitled only to
                                 the purchase price per Share listed on the
                                 front cover of this Offer to Purchase and Proxy
                                 Statement.
 
Payment Date..................   Promptly after the Expiration Date or any
                                 extension thereof (the "Payment Date").
 
Stock Transfer Tax............   Except as described herein, ILN will pay or
                                 cause to be paid any stock transfer taxes with
                                 respect to the sale and transfer of any Shares
                                 to it or its order pursuant to the Offer. Each
                                 Preferred Shareholder will be responsible for
                                 paying any income or gross receipts taxes
                                 imposed by any jurisdiction by reason of the
                                 Special Cash Payment and/or the sale of the
                                 Shares. See Instruction 6 of the applicable
                                 Letter of Transmittal and Proxy. See also
                                 "Terms of the Offer -- Acceptance of Shares for
                                 Payment and Payment of Purchase Price" and
                                 "Certain Federal Income Tax Consequences."
 
Further Information...........   Additional copies of this Offer to Purchase and
                                 Proxy Statement, the applicable Letter of
                                 Transmittal and Proxy, and the applicable
                                 separate Proxy may be obtained by contacting
                                 MacKenzie Partners, Inc., at (800) 322-2885
                                 (toll free) or (212) 929-5500 (brokers and
                                 dealers). Questions about the Offer should be
                                 directed to DLJ at (800) 334-1604 (toll free).
 
                                        6
<PAGE>   7
 
                                SPECIAL FACTORS
 
PURPOSE OF THE OFFER; CERTAIN EFFECTS OF THE OFFER
 
     ILN believes that the purchase of the Shares at this time represents an
attractive economic opportunity that will benefit ILN, its shareholders and IPC.
In addition, the Offer gives Preferred Shareholders the opportunity to sell
their Shares at a price which ILN believes to be a premium to the respective
market prices of Shares of each Series of Preferred on the date of the
announcement of the Offer and without the usual transaction costs associated
with a sale. ILN did not find it practicable to, and did not, quantify or
otherwise assign relative weights to these considerations. Trading of the Shares
of each Series of Preferred has been limited and sporadic. Therefore, ILN
determined the Purchase Price for each Series of Preferred with reference to
certain objective factors, including, but not limited to, historical and recent
market prices, yields on U.S. Treasury and municipal securities, yields on
comparable preferred securities, the prior trading characteristics of each
Series of Preferred, and the current and future redemption price of each Series
of Preferred, as well as certain subjective factors, including, but not limited
to, general industry outlook, general market supply of securities of similar
type, and supply and demand factors in the securities markets generally.
Although the weighing of these factors is subjective, ILN gave relatively more
weight to objective factors, such as yields on U.S. Treasury and municipal
securities, yields on comparable preferred securities, and current and future
redemption prices of the Series of Preferred.
 
     Neither ILN, IPC nor their respective boards of directors (individually, a
"Board of Directors" and collectively, the "Boards of Directors") received any
report, opinion or appraisal from an outside party which is related to the
Offer, including, but not limited to, any report, opinion or appraisal relating
to the consideration or the fairness of the consideration to be offered to the
holders of the Shares or the fairness of such Offer to ILN, IPC or the
unaffiliated holders of Shares. Neither of the Boards of Directors nor any
individual director of ILN or IPC has retained an unaffiliated representative to
act solely on behalf of unaffiliated holders of Shares for the purposes of
negotiating the terms of the Offer or preparing a report concerning the fairness
of the Offer. Neither ILN, IPC nor their respective Boards of Directors believed
these measures were necessary to ensure fairness in light of the fact that the
Offer will not result in a liquidation or change in control in ILN, IPC or any
of their affiliates.
 
     Preferred Shareholders are not under any obligation to tender Shares
pursuant to the Offer. The Offer does not constitute notice of redemption of any
Series of Preferred pursuant to IPC's Articles, nor does ILN or IPC intend to
effect any such redemption by making the Offer. Further, the Offer does not
constitute a waiver by IPC of any option it has to redeem Shares. The 4.08%
Series, 4.20% Series, 4.26% Series, 4.42% Series and 4.70% Series of cumulative
preferred stock are not subject to mandatory redemption, but presently are
redeemable at the option of IPC at $51.50 per Share, $52.00 per Share, $51.50
per Share, $51.50 per Share and $51.50 per Share respectively. The 7.75% Series
is also not subject to mandatory redemption and is not redeemable until July 1,
2003. On or after July 1, 2003, the 7.75% Series is redeemable at the option of
IPC at $50.00 per Share. The Shares of each Series of Preferred have no
preemptive or conversion rights. Upon liquidation or dissolution of IPC, owners
of the Shares would be entitled to receive an amount equal to the liquidation
preference of $50.00 per share plus all accrued and unpaid dividends (whether or
not earned or declared) thereon to the date of payment, prior to the payment of
any amounts to the holders of IPC's common stock (currently, ILN is the only
holder of IPC's common stock).
 
     Shares validly tendered to the Depositary pursuant to the Offer and not
withdrawn in accordance with the procedures set forth herein shall be held until
the Expiration Date (or returned to the extent the Offer is terminated in
accordance herewith). To the extent that the Proposed Amendment is adopted at
the Special Meeting and the Shares tendered are accepted for payment and paid
for in accordance with the terms hereof, ILN presently intends to sell or
otherwise transfer Shares to IPC and, at that time, it is expected that IPC
would retire and cancel the Shares. However, in the event the Proposed Amendment
is not adopted at the Special Meeting, ILN may elect to, but is not obligated
to, waive, subject to applicable law, such condition. In that case, subsequent
to ILN's waiver and purchase of the Shares, IPC anticipates, as promptly as
practicable thereafter, that it would call another special meeting of its
shareholders and solicit proxies therefrom for an amendment substantially
similar to the Proposed Amendment. At that meeting, ILN would vote any Shares
                                        7
<PAGE>   8
 
purchased by it pursuant to the Offer or otherwise (together with its shares of
IPC's common stock) in favor of such amendment, thereby maximizing the prospects
for the adoption of the amendment.
 
     The purchase of Shares of each Series of Preferred pursuant to the Offer
will reduce the number of holders of Shares and the number of such Shares that
might otherwise trade publicly, and, depending upon the number of Shares so
purchased, such reduction could adversely affect the ratings, liquidity and
market value of the remaining Shares of each such Series of Preferred held by
the public. The extent of the public market for such Shares and the availability
of price quotations would, however, depend upon such factors as the number of
shareholders remaining at such time, the interest in maintaining a market in the
Shares on the part of securities firms and other factors. As of [RECORD DATE],
there were           registered holders of the 4.08% Series,
registered holders of the 4.20% Series,           registered holders of the
4.26% Series,           registered holders of the 4.42% Series,
registered holders of the 4.70% Series and           registered holders of the
7.75% Series. Depending on the number of Shares tendered and purchased pursuant
to the Offer, the Series of Preferred listed and trading on the NYSE may no
longer meet the requirements of the NYSE for continued listing, which could
adversely affect the market for such Shares. In addition, each Series of
Preferred (other than the 7.75% Series) is currently registered under Section
12(b) of the Securities Exchange Act of 1934, as amended (the "Exchange Act").
Registration of such Shares under the Exchange Act may be terminated upon the
application by IPC to the SEC if such Shares are neither listed on a national
securities exchange nor held by more than 300 holders of record. Termination of
registration of such Shares under the Exchange Act would substantially reduce
the information required to be furnished to Preferred Shareholders and could
make certain provisions of the Exchange Act, such as the requirement of Rule
13e-3 thereunder with respect to "going private transactions," no longer
applicable to IPC.
 
     As of the date of this Offer to Purchase and Proxy Statement, each Series
of Preferred was rated Baa2, BBB- and BBB-, by Moody's Investors Service, Inc.
("Moody's), Standard & Poor's Rating Services ("S&P") and Duff & Phelps, Inc.
(D&P"), respectively.
 
LIQUIDITY OF TRADING MARKET
 
     To the extent that Shares of any Series of Preferred are tendered, accepted
for payment and paid for in the Offer, the trading market for Shares of such
Series of Preferred that remain outstanding may be significantly more limited,
which might adversely affect the liquidity, market value and price volatility of
such Shares. Equity securities with a smaller outstanding market value available
for trading (the "float") may command a lower price than would comparable equity
securities with a greater float. Therefore, the market price for Shares that are
not tendered in the Offer may be affected adversely to the extent that the
number of Shares purchased pursuant to the Offer reduces the float. A reduced
float may also make the trading price of the Shares that are not tendered,
accepted for payment and paid for in the Offer more volatile. Preferred
Shareholders of the remaining Shares may attempt to obtain quotations for the
Shares from their brokers; however, there can be no assurance that any trading
market will exist for such Shares following consummation of the Offer. To the
extent a market continues to exist for the Shares after the Offer, the Shares
may trade at a discount compared to present trading depending on the market for
shares with similar features, the performance of IPC and other factors. There is
no assurance that an active market in the Shares will exist and no assurance as
to the prices at which the Shares may trade.
 
POTENTIAL EFFECTS OF THE PROPOSED AMENDMENT ON NON-TENDERING PREFERRED
SHAREHOLDERS
 
     If the Proposed Amendment is adopted at the Special Meeting, Preferred
Shareholders of Shares that are not tendered and purchased pursuant to the Offer
will no longer be entitled to the benefits of the Debt Limitation Provision,
which will have been removed by the Proposed Amendment. As discussed above, the
Debt Limitation Provision places restrictions on IPC's ability to issue or
assume unsecured indebtedness. Although IPC's debt instruments may contain
certain restrictions on IPC's ability to issue or assume debt, any such
restrictions may be waived and the increased flexibility afforded IPC by the
removal of the Debt Limitation Provision may permit IPC to take certain actions
that may increase the credit risks with respect to IPC, adversely affecting the
market price and credit rating of the remaining Shares or otherwise be
materially adverse to the interests of the remaining Preferred Shareholders. In
addition, to the extent that IPC elects to
                                        8
<PAGE>   9
 
issue or assume additional unsecured indebtedness, the remaining Preferred
Shareholders' relative position in IPC's capital structure could be perceived to
decline, which in turn could adversely affect the market prices and credit
ratings of the remaining Shares.
 
PLANS OF ILN AND IPC AFTER THE OFFER
 
     Following the consummation of the Offer, the business and operations of IPC
are expected to be continued substantially as they are currently being
conducted. Except as disclosed herein, ILN and IPC currently have no plans or
proposals that relate to or would result in: (i) the acquisition by any person
or entity of additional securities of IPC or the disposition of securities of
IPC, other than in the ordinary course of business; (ii) an extraordinary
corporate transaction, such as a merger, reorganization or liquidation,
involving IPC or any of its subsidiaries; (iii) a sale or transfer of a material
amount of assets of IPC or any of its subsidiaries; (iv) any change in the
present Board of Directors or management of IPC; (v) any material change in the
present dividend rate or policy, or indebtedness or capitalization of IPC; (vi)
any other material change in IPC's corporate structure or business; (vii) any
change in IPC's Articles or by-laws ("By-laws") or any actions that may impede
the acquisition of control of IPC by any person; (viii) a class of equity
securities of IPC being delisted from a national securities exchange or no
longer authorized to be quoted on the OTC; (ix) a class of equity securities of
IPC becoming eligible for termination of registration pursuant to Section
12(g)(4) of the Exchange Act; or (x) the suspension of IPC's obligation to file
reports pursuant to Section 15(d) of the Exchange Act. However, ILN and IPC have
from time to time considered, and expect to consider in the future, various
strategies designed to enhance IPC's ability to anticipate and adapt to changes
in the increasingly competitive utility industry. ILN and IPC are currently
developing strategies responsive to the enactment of Public Act 90-561 ("PA
90-561") in Illinois on December 16, 1997. PA 90-561 amends the Illinois Public
Utilities Act in numerous respects and provides a comprehensive framework for
restructuring the electric utility industry in Illinois, including a managed
transition to a competitive industry. PA 90-561 permits electric utilities in
Illinois, including IPC, upon approval of the Illinois Commerce Commission
("ICC"), to issue, directly or indirectly, securitization bonds on or after
August 1, 1998 in an aggregate amount not to exceed, among certain other
restrictions, 50% of the electric utility's total capitalization as of December
31, 1996, with the proceeds of such issuance generally limited to the
refinancing of debt or equity of the electric utility. IPC intends to file an
application with the ICC seeking the approvals required for such issuance of
securitization bonds and may determine to proceed with such issuance in 1998. In
addition, ILN and IPC may pursue other business strategies, including business
combinations with other companies, internal restructurings involving the
complete or partial separation of IPC's generation, transmission and
distribution businesses, acquisitions or dispositions of assets or lines of
business, and additions to or reductions of franchised service territories. ILN
and IPC may from time to time engage in discussions, either internally or with
third parties, regarding one or more of these potential strategies. Those
discussions may be subject to confidentiality agreements and the policy of ILN
and IPC is generally not to comment on such activities. No assurances can be
given that any potential transaction of the types described above may actually
occur, or if one does occur, no assurances can be given with respect to the
ultimate effect of any such transaction on ILN's or IPC's results or operations,
financial condition or competitive position.
 
     After the consummation of the Offer, ILN or IPC, in its sole discretion,
may purchase additional Shares on the open market, in privately negotiated
transactions, through one or more tender offers or otherwise. Any such purchases
may be on the same terms as, or on terms which are more or less favorable to
holders of Shares than, the terms of the Offer. However, Rule 13e-4(f)(6) under
the Exchange Act, prohibits ILN and its affiliates (including IPC) from
purchasing any Shares of a Series of Preferred, other than pursuant to the
Offer, until at least ten business days after the Expiration Date with respect
to that Series of Preferred. Any future purchases of Shares by ILN or IPC would
depend on many factors, including the success of the Offer, the market price of
the Shares, ILN's business and financial position, legal restrictions on ILN's
ability to purchase Shares as well as general economic and market conditions.
 
     NEITHER ILN, IPC, THEIR RESPECTIVE BOARDS OF DIRECTORS, NOR ANY OF THEIR
RESPECTIVE OFFICERS MAKES ANY RECOMMENDATION TO ANY PREFERRED SHAREHOLDER AS TO
WHETHER TO TENDER ANY OR ALL SHARES. EACH PREFERRED
 
                                        9
<PAGE>   10
 
SHAREHOLDER MUST MAKE HIS OR HER OWN DECISION AS TO WHETHER TO TENDER
SHARES AND, IF SO, HOW MANY SHARES TO TENDER.
 
CERTAIN LEGAL MATTERS; REGULATORY APPROVALS
 
     Neither ILN nor IPC needs to obtain approval from the ICC to undertake the
Offer or the proxy solicitation. ILN is not aware of any license or regulatory
permit that would be material to ILN's or IPC's business that might be adversely
affected by ILN's acquisition of Shares as contemplated in the Offer or of any
other approval or other action by any government or governmental, administrative
or regulatory authority or agency, domestic or foreign, that would be required
for ILN's acquisition of Shares pursuant to the Offer. Should any approval or
other action be required, ILN currently contemplates that it will seek such
approval or other action. ILN cannot predict whether it could be required to
delay the acceptance for payment of, or payment for, Shares tendered pursuant to
the Offer pending the outcome of any such matter. There can be no assurance that
any such approval or other action, if needed, would be obtained, or would be
obtained without substantial conditions or that the failure to obtain any such
approval or other action might not result in adverse consequences to ILN's or
IPC's business. ILN intends to make all required filings under the Exchange Act.
ILN's obligation under the Offer to accept for payment, or make payment for,
Shares is subject to certain conditions. See "Terms of the Offer -- Certain
Conditions of the Offer."
 
     Except for adoption of the Proposed Amendment, which condition can be
waived by ILN, no approval of the holders of any Shares or the holders of any of
IPC's other securities or the holders of ILN's securities is required in
connection with the Offer. See "Proposed Amendment and Proxy Solicitation."
 
DISSENTERS' RIGHTS
 
     No dissenters' rights are available to holders of Shares in connection with
the Offer. However, holders of Shares may be entitled to dissenters' rights in
connection with the adoption of the Proposed Amendment. See "Proposed Amendment
and Proxy Solicitation -- Dissenters' Rights."
 
                               TERMS OF THE OFFER
 
NUMBER OF SHARES; PURCHASE PRICES; EXPIRATION DATE; DIVIDENDS
 
     Upon the terms and subject to the conditions described herein and in the
applicable Letter of Transmittal, ILN will purchase any and all Shares that are
validly tendered on or prior to the Expiration Date (and not properly withdrawn
in accordance with "Terms of the Offer -- Withdrawal Rights") at the purchase
price per Share listed on the front cover of this Offer to Purchase and Proxy
Statement for the Shares tendered, net to the seller in cash. See "Terms of the
Offer -- Certain Conditions of the Offer" and "Terms of the Offer -- Extension
of Tender Period; Termination; Amendments." On             , there were issued
and outstanding 283,290 Shares of the 4.08% Series of Preferred; 167,720 Shares
of the 4.20% Series of Preferred; 136,000 Shares of the 4.26% Series of
Preferred; 134,400 Shares of the 4.42% Series of Preferred; 176,000 Shares of
the 4.70% Series of Preferred; and 241,700 Shares of the 7.75% Series of
Preferred.
 
     THE OFFER FOR A SERIES OF PREFERRED IS NOT CONDITIONED UPON ANY MINIMUM
NUMBER OF SHARES OF SUCH SERIES OF PREFERRED BEING TENDERED AND IS INDEPENDENT
OF THE OFFER FOR ANY OTHER SERIES OF PREFERRED. THE OFFER, HOWEVER, IS
CONDITIONED UPON, AMONG OTHER THINGS, THE PROPOSED AMENDMENT, AS DESCRIBED
HEREIN, BEING ADOPTED AT THE SPECIAL MEETING. SEE "TERMS OF THE OFFER -- CERTAIN
CONDITIONS OF THE OFFER."
 
     The Offer is being sent to all persons in whose names Shares are registered
on the books of IPC as of the close of business on [RECORD DATE] and transferees
of such persons. Only a record holder of Shares on the Record Date may vote in
person or by proxy at the Special Meeting. No record date is fixed for
determining which persons are permitted to tender Shares. Any person who is the
beneficial owner but not the record holder of Shares must arrange for the record
transfer of such Shares prior to tendering.
 
                                       10
<PAGE>   11
 
     With respect to each Series of Preferred, the Expiration Date is the later
of 5:00 p.m. New York City time, on [EXPIRATION DATE] or the latest time and
date to which the Offer with respect to such Series of Preferred is extended.
ILN expressly reserves the right, in its sole discretion, and at any time and/or
from time to time, to extend the period of time during which the Offer for any
Series of Preferred is open, by giving oral or written notice of such extension
to the Depositary and making a public announcement thereof, without extending
the period of time during which the Offer for any other Series of Preferred is
open. There is no assurance whatsoever that ILN will exercise its right to
extend the Offer for any Series of Preferred. If ILN decides, in its sole
discretion, to (i) decrease the number of Shares of any Series of Preferred
being sought, (ii) increase or decrease the consideration offered in the Offer
to holders of any Series of Preferred or (iii) increase or decrease the
Soliciting Dealers' fees and, at the time that notice of such increase or
decrease is first published, sent or given to holders of such Series of
Preferred in the manner specified herein, the Offer for such Series of Preferred
is scheduled to expire at any time earlier than the tenth business day from the
date that such notice is first so published, sent or given, such Offer will be
extended until the expiration of such ten-business-day period. For purposes of
the Offer, a "business day" means any day other than a Saturday, Sunday or
federal holiday and consists of the time period from 12:01 a.m. through 12:00
midnight, New York City time.
 
      NO ALTERNATIVE, CONDITIONAL OR CONTINGENT TENDERS WILL BE ACCEPTED.
 
     The May 1998 Dividend has been declared on each Series of Preferred,
payable May 1, 1998 to holders of record as of the close of business on April 9,
1998. A tender and purchase of Shares pursuant to the Offer will not deprive
such Preferred Shareholder of his or her right to receive the May 1998 Dividend
on his or her Shares held of record on April 9, 1998, regardless of when such
tender is made. Tendering Preferred Shareholders will not be entitled to any
dividends in respect of any dividend period (or any portion thereof) after May
1, 1998. The payment of the May 1998 Dividend will be made separately from
payments for Shares tendered in the Offer or the payment of any Special Cash
Payments.
 
PROCEDURE FOR TENDERING SHARES
 
     To tender Shares pursuant to the Offer, the tendering owner of Shares must
either:
 
          (i) send to the Depositary (at one of its addresses set forth on the
     back cover of this Offer to Purchase and Proxy Statement) a properly
     completed and duly executed Letter of Transmittal and Proxy, or facsimile
     thereof, together with any required signature guarantees and any other
     documents required by the Letter of Transmittal and Proxy and either (a)
     certificates for the Shares to be tendered must be received by the
     Depositary at one of such addresses or (b) such Shares must be delivered
     pursuant to the procedures for book-entry transfer described herein (and a
     confirmation of such delivery must be received by the Depositary), in each
     case by 5:00 p.m., New York City time, on the Expiration Date; or
 
          (ii) comply with the guaranteed delivery procedure described under
     "Guaranteed Delivery Procedure" below.
 
A tender of Shares made pursuant to any method of delivery set forth herein or
in the Letter of Transmittal and Proxy will constitute a binding agreement
between the tendering holder and ILN upon the terms and subject to the
conditions of the Offer.
 
     The Depositary will establish an account with respect to the Shares at The
Depository Trust Company (the "Book-Entry Transfer Facility") for purposes of
the Offer within two business days after the date of this Offer to Purchase and
Proxy Statement, and any financial institution that is a participant in the
system of a Book-Entry Transfer Facility may make delivery of Shares by causing
the Book-Entry Transfer Facility to transfer such Shares into the Depositary's
account in accordance with the procedures of the Book-Entry Transfer Facility.
Although delivery of Shares may be effected through book-entry transfer, such
delivery must be accompanied by either (i) a properly completed and duly
executed Letter of Transmittal and Proxy, together with any required signature
guarantees and any other required documents or (ii) an Agent's Message
 
                                       11
<PAGE>   12
 
(as hereinafter defined) and, in any case, must be received by the Depositary at
one of its addresses set forth on the back cover of this Offer to Purchase and
Proxy Statement on or prior to the Expiration Date. The confirmation of a book
entry transfer of Shares into the Depositary's account at the Book-Entry
Transfer Facility as described above is referred to as a "Book-Entry
Confirmation."
 
     DELIVERY OF THE LETTER OF TRANSMITTAL AND PROXY AND ANY OTHER REQUIRED
DOCUMENTS TO THE BOOK-ENTRY TRANSFER FACILITY OR TO ILN DOES NOT CONSTITUTE
DELIVERY TO THE DEPOSITARY.
 
     The term "Agent's Message" means a message, transmitted by the Book-Entry
Transfer Facility, received by the Depositary and forming a part of the
book-entry transfer when a tender is initiated, which states that the Book-Entry
Transfer Facility has received an express acknowledgment from a participant
tendering Shares, that such participant has received and agrees to be bound by
the terms of the Letter of Transmittal and Proxy and that ILN may enforce such
agreement against such participant.
 
     Signature Guarantees. Except as otherwise provided below, all signatures on
a Letter of Transmittal and Proxy must be guaranteed by a firm that is a member
in good standing of a registered national securities exchange or the National
Association of Securities Dealers, Inc. ("NASD"), or by a commercial bank or
trust company having an office or correspondent in the United States that is a
participant in an approved Signature Guarantee Medallion Program (each of the
foregoing being referred to as an "Eligible Institution"). Signatures on a
Letter of Transmittal and Proxy need not be guaranteed if (i) the Letter of
Transmittal and Proxy is signed by the registered owner of the Shares tendered
therewith and such owner has not completed the box entitled "Special Payment
Instructions" or the box entitled "Special Delivery Instructions" on the Letter
of Transmittal and Proxy or (ii) such Shares are tendered for the account of an
Eligible Institution. See Instructions 1 and 5 of the Letter of Transmittal and
Proxy. If Shares are registered in the name of a person other than the signatory
on the Letter of Transmittal and Proxy, or if unpurchased Shares are to be
issued to a person other than the registered holder(s), the certificates must be
endorsed or accompanied by appropriate stock powers, in either case signed
exactly as the name or names of the registered holder(s) appear on the Shares
with the signature(s) on the Shares or stock powers guaranteed as stated above.
See Instructions 4, 6 and 7 to the Letter of Transmittal and Proxy.
 
     Guaranteed Delivery Procedure. If a Preferred Shareholder desires to tender
Shares pursuant to the Offer and such Preferred Shareholder's certificates are
not immediately available or the procedures for book-entry transfer cannot be
completed on a timely basis or time will not permit all required documents to
reach the Depositary prior to the Expiration Date, such Shares may nevertheless
be tendered if all of the following guaranteed delivery procedures are complied
with:
 
          (i) such tender is made by or through an Eligible Institution;
 
          (ii) a properly completed and duly executed Notice of Guaranteed
     Delivery, substantially in the form provided by ILN and IPC herewith, is
     received (with any required signatures or signature guarantees) by the
     Depositary as provided below on or prior to 5:00 p.m., New York City time,
     on the Expiration Date; and
 
          (iii) the certificates for all tendered Shares in proper form for
     transfer or a Book-Entry Confirmation with respect to all tendered Shares,
     together with a properly completed and duly executed Letter of Transmittal
     and Proxy, or a manually signed facsimile thereof, and any other documents
     required by the Letter of Transmittal and Proxy, are received by the
     Depositary no later than 5:00 p.m., New York City time, within three
     business days after the date of execution of such Notice of Guaranteed
     Delivery.
 
     THE NOTICE OF GUARANTEED DELIVERY MAY BE DELIVERED BY HAND OR MAILED OR
TRANSMITTED BY FACSIMILE TO THE DEPOSITARY AND MUST INCLUDE AN ENDORSEMENT BY AN
ELIGIBLE INSTITUTION IN THE FORM SET FORTH IN SUCH NOTICE OF GUARANTEED
DELIVERY.
 
     In all cases, Shares shall not be deemed validly tendered unless a properly
completed and duly executed Letter of Transmittal and Proxy, a manually signed
facsimile thereof, or, if applicable, an Agent's Message, is received by the
Depositary.
 
                                       12
<PAGE>   13
 
     Notwithstanding any other provision hereof, payment for Shares accepted for
payment pursuant to the Offer in all cases will be made only after timely
receipt by the Depositary of certificates for (or an Agent's Message with
respect to) such Shares, a Letter of Transmittal and Proxy, properly completed
and duly executed, or a manually signed facsimile thereof, with any required
signature guarantees and all other documents required by the Letter of
Transmittal and Proxy. Accordingly, tendering Preferred Shareholders may be paid
at different times depending upon when certificates for Shares or Book-Entry
Confirmations are actually received by the Depositary. Under no circumstances
will interest be paid on the Purchase Price for Shares tendered to ILN pursuant
to the Offer, regardless of any extension of the Offer or any delay in making
such payment.
 
     THE METHOD OF DELIVERY OF SHARES AND ALL OTHER REQUIRED DOCUMENTS IS AT THE
OPTION AND RISK OF THE TENDERING PREFERRED SHAREHOLDER. IF DELIVERY IS BY MAIL,
REGISTERED MAIL WITH RETURN RECEIPT REQUESTED, PROPERLY INSURED, IS RECOMMENDED.
BECAUSE IT IS THE TIME OF RECEIPT, NOT THE TIME OF MAILING, WHICH DETERMINES
WHETHER A TENDER HAS BEEN MADE PRIOR TO THE EXPIRATION DATE, SUFFICIENT TIME
SHOULD BE ALLOWED TO ASSURE TIMELY DELIVERY.
 
     TO AVOID FEDERAL INCOME TAX BACKUP WITHHOLDING EQUAL TO 31% OF THE GROSS
PAYMENTS MADE PURSUANT TO THE OFFER, EACH TENDERING PREFERRED SHAREHOLDER WHO IS
A UNITED STATES PERSON MUST NOTIFY THE DEPOSITARY OF SUCH PREFERRED
SHAREHOLDER'S CORRECT TAXPAYER IDENTIFICATION NUMBER AND PROVIDE CERTAIN OTHER
INFORMATION BY PROPERLY COMPLETING AND EXECUTING THE SUBSTITUTE FORM W-9
INCLUDED IN THE LETTER OF TRANSMITTAL AND PROXY OR IN THE SEPARATE PROXY (OR, IN
THE CASE OF A FOREIGN PREFERRED SHAREHOLDER, FORM W-8 OBTAINABLE FROM THE
DEPOSITARY). SEE "CERTAIN FEDERAL INCOME TAX CONSEQUENCES."
 
     EACH PREFERRED SHAREHOLDER IS URGED TO CONSULT WITH HIS OR HER OWN TAX
ADVISOR REGARDING THE TAX CONSEQUENCES OF THE OFFER.
 
     Determinations of Validity. All questions as to the form of documents and
the validity, eligibility (including the time of receipt) and acceptance for
payment of any tender of Shares will be determined by ILN, in its sole
discretion, and its determination will be final and binding. ILN reserves the
absolute right to reject any or all tenders of Shares that (i) it determines are
not in proper form or (ii) the acceptance for payment of or payment for which
may, in the opinion of ILN's counsel, be unlawful. ILN also reserves the
absolute right to waive any defect or irregularity in any tender of Shares. No
tender of Shares will be deemed to be properly made until all defects or
irregularities have been cured or waived. None of ILN, IPC, the Dealer Manager,
the Depositary, the Information Agent or any other person will be under any duty
to give notice of any defect or irregularity in tenders, nor shall any of them
incur any liability for failure to give any such notice.
 
WITHDRAWAL RIGHTS
 
     Tenders of Shares made pursuant to the Offer may be withdrawn at any time
prior to the Expiration Date. Thereafter, such tenders are irrevocable, except
that they may be withdrawn after                     , 1998 unless previously
accepted for payment as provided in this Offer to Purchase and Proxy Statement.
 
     The proxy accompanying any tendered Shares that are withdrawn will not be
considered revoked unless the Preferred Shareholder specifically revokes such
proxy as described herein. See "Proposed Amendment and Proxy Solicitation --
Proxies."
 
     To be effective, a written or facsimile notice of withdrawal must be timely
received by the Depositary, at one of its addresses set forth on the back cover
of this Offer to Purchase and Proxy Statement, and must specify the name of the
person who tendered the Shares to be withdrawn and the number of Shares to be
withdrawn. If the Shares to be withdrawn have been delivered to the Depositary,
a signed notice of withdrawal
 
                                       13
<PAGE>   14
 
with signatures guaranteed by an Eligible Institution (except in the case of
Shares tendered by an Eligible Institution) must be submitted prior to the
release of such Shares. In addition, such notice must specify, in the case of
Shares tendered by delivery of certificates, the name of the registered owner
(if different from that of the tendering Preferred Shareholder) and the serial
numbers shown on the particular certificates evidencing the Shares to be
withdrawn or, in the case of Shares tendered by book-entry transfer, the name
and number of the account at the Book-Entry Transfer Facility to be credited
with the withdrawn Shares and the name of the registered holder (if different
from the name of such account). Withdrawals may not be rescinded, and Shares
withdrawn will thereafter be deemed not validly tendered for purposes of the
Offer. However, withdrawn Shares may be re-tendered by again following one of
the procedures described in "Terms of the Offer -- Procedure for Tendering
Shares" at any time prior to the Expiration Date.
 
     All questions as to the form and validity (including time of receipt) of
any notice of withdrawal will be determined by ILN, in its sole discretion, and
its determination will be final and binding. None of ILN, IPC, the Dealer
Manager, the Depositary, the Information Agent or any other person will be under
any duty to give notification of any defect or irregularity in any notice of
withdrawal or will incur any liability for failure to give any such
notification.
 
ACCEPTANCE OF SHARES FOR PAYMENT AND PAYMENT OF PURCHASE PRICE
 
     Upon the terms and subject to the conditions of the Offer, and as promptly
as practicable after the Expiration Date, ILN will accept for payment (and
thereby purchase) and pay for Shares validly tendered and not withdrawn as
permitted in "Terms of the Offer -- Withdrawal Rights." Thereafter, payment for
all Shares validly tendered on or prior to the Expiration Date and accepted
pursuant to the Offer will be made by the Depositary as promptly as practicable
after the Expiration Date. In all cases, payment for Shares accepted for payment
pursuant to the Offer will be made promptly but only after timely receipt by the
Depositary of certificates for such Shares (or of an Agent's Message), a
properly completed and duly executed Letter of Transmittal and Proxy (or in the
case of an Eligible Institution, a facsimile thereof) and any other required
documents. Accordingly, tendering Preferred Shareholders may be paid at
different times depending upon when Share certificates or Book-Entry
Confirmations are actually received by the Depositary.
 
     For purposes of the Offer, ILN will be deemed to have accepted for payment
(and thereby purchased) Shares that are validly tendered and not withdrawn as,
if and when it gives oral or written notice to the Depositary of its acceptance
for payment of such Shares. ILN will pay for Shares that it has purchased
pursuant to the Offer by depositing the purchase price therefor thereon with the
Depositary, which will act as agent for tendering Preferred Shareholders for the
purpose of receiving payment from ILN and transmitting payment to tendering
Preferred Shareholders. UNDER NO CIRCUMSTANCES WILL INTEREST BE PAID ON AMOUNTS
TO BE PAID TO TENDERING PREFERRED SHAREHOLDERS, REGARDLESS OF ANY DELAY IN
MAKING SUCH PAYMENT.
 
     Certificates for all Shares not validly tendered will be returned or, in
the case of Shares tendered by book-entry transfer, such Shares will be credited
to an account maintained with the Book-Entry Transfer Facility, as promptly as
practicable, without expense to the tendering Preferred Shareholder.
 
     Payment for Shares may be delayed in the event of difficulty in determining
the number of Shares properly tendered. If certain events occur, ILN may not be
obligated to purchase Shares pursuant to the Offer. See "Terms of the Offer --
Certain Conditions of the Offer."
 
     ILN will pay or cause to be paid any stock transfer taxes with respect to
the sale and transfer of any Shares to it or its order pursuant to the Offer.
If, however, payment of the purchase price is to be made to, or Shares not
tendered or not purchased are to be registered in the name of, any person other
than the registered owner, or if tendered Shares are registered in the name of
any person other than the person signing the Letter of Transmittal and Proxy,
the amount of any stock transfer taxes (whether imposed on the registered owner,
such other person or otherwise) payable on account of the transfer to such
person will be deducted from the purchase price unless satisfactory evidence of
the payment of such taxes, or exemption therefrom, is submitted. Each Preferred
Shareholder will be responsible for paying any income or gross receipts taxes
imposed by any jurisdiction by reason of the sale of the Shares or the Special
Cash Payment, as described
 
                                       14
<PAGE>   15
 
herein. See Instruction 6 of the accompanying Letter of Transmittal and Proxy.
See also "Proposed Amendment and Proxy Solicitation -- Special Cash Payments"
and "Certain Federal Income Tax Consequences."
 
CERTAIN CONDITIONS OF THE OFFER
 
     ILN WILL NOT BE REQUIRED TO ACCEPT FOR PAYMENT OR PAY FOR ANY SHARES
TENDERED IF THE PROPOSED AMENDMENT IS NOT ADOPTED AT THE SPECIAL MEETING.
PREFERRED SHAREHOLDERS OF RECORD HAVE THE RIGHT TO VOTE FOR OR AGAINST THE
PROPOSED AMENDMENT REGARDLESS OF WHETHER THEY TENDER THEIR SHARES. IF THE
PROPOSED AMENDMENT IS ADOPTED AT THE SPECIAL MEETING, IPC WILL MAKE A SPECIAL
CASH PAYMENT TO EACH PREFERRED SHAREHOLDER WHO VOTED IN FAVOR OF THE PROPOSED
AMENDMENT, PROVIDED THAT THEIR SHARES HAVE NOT BEEN TENDERED PURSUANT TO THE
OFFER. PREFERRED SHAREHOLDERS WHO TENDER THEIR SHARES WILL ONLY BE ENTITLED TO
THE PURCHASE PRICE PER SHARE LISTED ON THE FRONT COVER OF THIS OFFER TO PURCHASE
AND PROXY STATEMENT.
 
     In addition, notwithstanding any other provision of the Offer, ILN will not
be required to accept for payment or pay for any Shares tendered, and may
terminate or amend the Offer (by oral or written notice to the Depositary and
timely public announcement) or may postpone (subject to the requirements of the
Exchange Act for prompt payment for or return of Shares) the acceptance for
payment of, or payment for, Shares tendered, if at any time on or after [DAY
BEFORE STATEMENT DATE], and at or before the Expiration Date, any of the
following shall have occurred (which shall not have been waived by ILN):
 
          (i) there shall have been threatened, instituted or pending any action
     or proceeding by any government or governmental, regulatory or
     administrative agency, authority or tribunal or any other person, domestic
     or foreign, or before any court, authority, agency or tribunal that (a)
     challenges the acquisition of Shares pursuant to the Offer or otherwise in
     any manner relates to or affects the Offer or (b) in the reasonable
     judgment of ILN, would or might materially and adversely affect the
     business, condition (financial or otherwise), income, operations or
     prospects of ILN and its subsidiaries taken as a whole, or otherwise
     materially impair in any way the contemplated future conduct of the
     business of ILN or any of its subsidiaries or materially impair the Offer's
     contemplated benefits to ILN;
 
          (ii) there shall have been any action threatened, pending or taken, or
     approval withheld, or any statute, rule, regulation, judgment, order or
     injunction threatened, proposed, sought, promulgated, enacted, entered,
     amended, enforced or deemed to be applicable to the Offer or ILN or any of
     its subsidiaries, by any legislative body, court, authority, agency or
     tribunal that, in ILN's reasonable judgment, would or might directly or
     indirectly (a) make the acceptance for payment of, or payment for, some or
     all of the Shares illegal or otherwise restrict or prohibit consummation of
     the Offer; (b) delay or restrict the ability of ILN, or render ILN unable,
     to accept for payment or pay for some or all of the Shares; (c) materially
     impair the contemplated benefits of the Offer to ILN or IPC (including
     materially increasing the effective interest cost of certain types of
     unsecured indebtedness); or (d) materially affect the business, condition
     (financial or otherwise), income, operations or prospects of ILN and its
     subsidiaries taken as a whole, or otherwise materially impair in any way
     the contemplated future conduct of the business of ILN or any of its
     subsidiaries;
 
          (iii) there shall have occurred (a) any significant decrease in the
     market price of the Shares, (b) any change in the general political,
     market, economic or financial conditions in the United States or abroad
     that, in the reasonable judgment of ILN, would or might have a material
     adverse effect on ILN's business, operations, prospects or ability to
     obtain financing generally or the trading in the Shares or other equity
     securities of ILN; (c) the declaration of a banking moratorium or any
     suspension of payments in respect of banks in the United States or any
     limitation on, or any event that, in ILN's reasonable judgment, would or
     might affect the extension of credit by lending institutions in the United
     States; (d) the commencement of war, armed hostilities or other
     international or national calamity directly or
 
                                       15
<PAGE>   16
 
     indirectly involving the United States; (e) any general suspension of
     trading in, or limitation on prices for, securities on any national
     securities exchange or in the over-the-counter market; (f) in the case of
     any of the foregoing existing at the time of the commencement of the Offer,
     in ILN's reasonable judgment, a material acceleration or worsening thereof,
     (g) any decline in either the Dow Jones Industrial Average or the Standard
     and Poor's Composite 500 Stock Index by an amount in excess of 15% measured
     from the close of business on [DAY BEFORE STATEMENT DATE]; or (h) a decline
     in the ratings accorded any of ILN's securities or the Shares by Moody's,
     S&P or D&P, or that S&P, Moody's or D&P has announced that it has placed
     any such rating under surveillance or review with negative implications;
 
          (iv) any tender or exchange offer with respect to some or all of the
     Shares (other than the Offer) or other equity securities of ILN, or a
     merger, acquisition or other business combination proposal for ILN, shall
     have been proposed, announced or made by any person or entity; or
 
          (v) there shall have occurred any event or events that have resulted,
     or, in ILN's reasonable judgment, may result, in an actual or threatened
     change in the business, condition (financial or otherwise), income,
     operations, stock ownership or prospects of ILN and its subsidiaries;
 
and in the sole judgment of ILN, such event or events make it undesirable or
inadvisable to proceed with the Offer or with such acceptance for payment or
payment.
 
     The foregoing conditions (including the condition that the Proposed
Amendment be adopted at the Special Meeting) are for the sole benefit of ILN and
may be asserted by ILN regardless of the circumstances (including any action or
inaction by ILN) giving rise to any such condition, and any such condition may
be waived by ILN, in whole or in part, at any time and from time to time in its
sole discretion. A decision by ILN to terminate or otherwise amend any Offer,
following the occurrence of any of the foregoing, with respect to one Series of
Preferred will not create an obligation on behalf of ILN to terminate or
otherwise amend in a similar manner the Offer with respect to any other Series
of Preferred. The failure by ILN at any time to exercise any of the foregoing
rights shall not be deemed a waiver of any such right and each such right shall
be deemed an ongoing right which may be asserted at any time and from time to
time. Any determination by ILN concerning the events described above will be
final and binding on all parties.
 
EXTENSION OF TENDER PERIOD; TERMINATION; AMENDMENTS
 
     ILN expressly reserves the right, in its sole discretion, and at any time
and/or from time to time prior to the Expiration Date, to extend the period of
time during which the Offer for any Series of Preferred is open by giving oral
or written notice of such extension to the Depositary, without extending the
period of time during which the Offer for any other Series of Preferred is open.
There can be no assurance, however, that ILN will exercise its right to extend
the Offer for any Series of Preferred. During any such extension, all Shares of
the subject Series of Preferred previously tendered will remain subject to the
Offer, except to the extent that such Shares may be withdrawn as set forth in
"Terms of the Offer -- Withdrawal Rights."
 
     ILN also expressly reserves the right, in its sole discretion, to, among
other things, terminate the Offer and not accept for payment or pay for any
Shares tendered, subject to Rule 13e-4(f) (5) under the Exchange Act, which
requires ILN either to pay the consideration offered or to return the Shares
tendered promptly after the termination or withdrawal of the Offer upon the
occurrence of any of the conditions specified in "Terms of the Offer -- Certain
Conditions of the Offer" by giving oral or written notice of such termination to
the Depositary, and making a public announcement thereof.
 
     Subject to compliance with applicable law, ILN further reserves the right,
in its sole discretion, to amend the Offer in any respect. Amendments to the
Offer may be made at any time and/or from time to time effected by public
announcement thereof, such announcement, in the case of an extension, to be
issued no later than 9:00 a.m., New York City time, on the next business day
after the previously scheduled Expiration Date. Any public announcement made
pursuant to the Offer will be disseminated promptly to Preferred Shareholders
affected thereby in a manner reasonably designed to inform such Preferred
Shareholders of such change. Without limiting the manner in which ILN may choose
to make a public announcement, except as
 
                                       16
<PAGE>   17
 
required by applicable law, ILN shall have no obligation to publish, advertise
or otherwise communicate any such public announcement other than by making a
release to the Dow Jones News Service.
 
     If ILN materially changes the terms of the Offer or the information
concerning the Offer, or if it waives a material condition of the Offer, ILN
will extend the Offer to the extent required by Rules 13e-4(d) (2) and 13e-4(e)
(2) under the Exchange Act. Those rules require that the minimum period during
which the Offer must remain open following material changes in the terms of the
Offer or information concerning the Offer (other than a change in price, a
change in percentage of securities sought or a change in the dealerIs
solicitation fee) will depend on the facts and circumstances, including the
relative materiality of such terms or information. The SEC has stated that, in
its view, an offer should remain open for a minimum of five business days from
the date that a notice of such a material change is first published, sent or
given. If the Offer is scheduled to expire at any time earlier than the
expiration of a period ending on the tenth business day from, and including, the
date that ILN publishes, sends or gives to Preferred Shareholders a notice that
it will (i) increase or decrease the price it will pay for Shares, (ii) decrease
the percentage of Shares it seeks or (iii) increase or decrease the Soliciting
Dealers' Fees, the Offer will be extended until the expiration of such period of
ten business days. THE OFFER FOR EACH SERIES OF PREFERRED IS INDEPENDENT OF THE
OFFER FOR ANY OTHER SERIES OF PREFERRED. IF ILN EXTENDS OR AMENDS ANY OFFER WITH
RESPECT TO ONE SERIES OF PREFERRED FOR ANY REASON, ILN WILL HAVE NO OBLIGATION
TO EXTEND THE OFFER FOR ANY OTHER SERIES OF PREFERRED.
 
                   PROPOSED AMENDMENT AND PROXY SOLICITATION
 
INTRODUCTION
 
     This Offer to Purchase and Proxy Statement is first being mailed on or
about [STATEMENT DATE] to the Preferred Shareholders of IPC in connection with
the solicitation of proxies by the Board of Directors of IPC (the "Board") for
use at the Special Meeting. At the Special Meeting, the shareholders of record
of IPC will vote upon the Proposed Amendment to the Articles.
 
     While Preferred Shareholders who wish to tender their Shares pursuant to
the Offer are not required to vote in favor of the Proposed Amendment, the Offer
is conditioned upon the Proposed Amendment being adopted at the Special Meeting.
In addition, Preferred Shareholders have the right to vote for the Proposed
Amendment regardless of whether they tender their Shares. If the Proposed
Amendment is adopted at the Special Meeting, IPC will make a special cash
payment in the amount of $     per Share (the "Special Cash Payment") to each
Preferred Shareholder who voted in favor of the Proposed Amendment, provided
that such Shares have not been tendered pursuant to the Offer. If a Preferred
Shareholder votes against the Proposed Amendment or abstains, such Preferred
Shareholder shall not be entitled to the Special Cash Payment (regardless of
whether the Proposed Amendment is adopted). Those Preferred Shareholders who
validly tender their Shares will be entitled only to the purchase price per
Share listed on the front cover of this Offer to Purchase and Proxy Statement.
See "-- Special Cash Payments."
 
VOTING SECURITIES, RIGHTS AND PROCEDURES
 
     Only holders of record of IPC's voting securities at the close of business
on [RECORD DATE] (the "Record Date") will be entitled to vote in person or by
proxy at the Special Meeting. The outstanding voting securities of IPC are
divided into two classes: common stock and cumulative preferred stock (par value
$50 per Share). The class of cumulative preferred stock has been issued in the
six Series of Preferred with the record holders of all Shares of the cumulative
preferred stock voting together as one class. The shares outstanding as of the
Record Date, and the vote to which each share is entitled in consideration of
the Proposed Amendment, are as follows:
 
<TABLE>
<CAPTION>
                                                              SHARES       VOTES PER
                         CLASS                              OUTSTANDING      SHARE
                         -----                              -----------    ---------
<S>                                                         <C>            <C>
Common Stock (No Par Value).............................     66,215,292     1 vote
Cumulative Preferred Stock (Par Value $50 Per Share)....      1,139,110     1 vote
</TABLE>
 
                                       17
<PAGE>   18
 
     The affirmative votes of the holders of at least two-thirds of the
outstanding shares of IPC's (i) common stock and all Series of Cumulative
Preferred Stock, voting together as one class, and (ii) Cumulative Preferred
Stock, all Series voting together as one class, are required to approve the
Proposed Amendment to be presented at the Special Meeting. Abstentions and
broker non-votes will have the effect of votes against the Proposed Amendment.
ILN, WHICH OWNS ALL OF THE OUTSTANDING SHARES OF COMMON STOCK OF IPC, HAS
ADVISED IPC THAT IT INTENDS TO VOTE ALL OF THE OUTSTANDING SHARES OF COMMON
STOCK OF IPC IN FAVOR OF THE PROPOSED AMENDMENT.
 
     Votes at the Special Meeting will be tabulated preliminarily by the
Depositary. Inspectors of Election, duly appointed by the presiding officer of
the Special Meeting, will definitively count and tabulate the votes and
determine and announce the results at the Special Meeting. IPC has no
established procedure for confidential voting.
 
DISSENTERS' RIGHTS
 
     Section 11.65 of the Illinois Business Corporation Act of 1983, as amended
(the "Business Corporation Act"), provides that a shareholder of an Illinois
corporation is entitled to dissent from, and obtain payment for his or her
shares in the event of, among other things, an amendment of the corporation's
articles of incorporation that materially and adversely affects rights in
respect of a dissenter's shares because it alters or abolishes a preferential
right of such shares. As described herein, the Proposed Amendment would amend
the Articles to remove a covenant which provides that the issuance or assumption
of unsecured indebtedness for certain purposes above a certain threshold
requires the consent of the holders of at least a majority of the total number
of Shares then outstanding. To the extent that the Proposed Amendment is deemed
to alter or abolish a "preferential right" of the Shares within the meaning of
Section 11.65 of the Business Corporation Act, the Preferred Shareholders would
have the right to dissent from the Proposed Amendment and obtain payment of the
fair value of their Shares. Pursuant to Section 11.70 of the Business
Corporation Act, a Preferred Shareholder who elects to dissent from the Proposed
Amendment (a "Dissenter"), must deliver to IPC before                     , 1998
a written demand for payment of his or her Shares if the Proposed Amendment is
adopted at the Special Meeting. If a written demand is not received by that
date, the Dissenter will lose the right to dissent and thereby obtain payment
for his or her Shares. A Dissenter also will lose the right to dissent if the
Dissenter votes in favor of the Proposed Amendment at the Special Meeting.
 
     If the Proposed Amendment gives rise to dissenters' rights under Section
11.65 of the Business Corporation Act and is adopted at the Special Meeting, IPC
will advise any Dissenter meeting the foregoing eligibility requirements of its
opinion as to the estimated fair value of the Shares owned by the Dissenter,
together with supporting information and a commitment to pay for such Shares at
the estimated fair value. A Dissenter who does not agree with IPC's estimated
fair value of the Shares must notify IPC, within 30 days thereafter, of the
Dissenter's estimate of fair value. If, within 60 days thereafter, IPC and the
Dissenter have not agreed upon the fair value of the Shares and the interest
due, IPC must either pay the Dissenter the difference in value demanded by the
Dissenter or file a petition in circuit court requesting the court to determine
the fair value of the Shares and the interest due.
 
     The foregoing summary does not purport to be a complete statement of the
provisions of Sections 11.65 and 11.70 of the Business Corporation Act and is
qualified in its entirety by reference to the relevant portions of such
Sections, copies of which are attached hereto as Attachment A.
 
     A Dissenter who receives payment for his or her Shares upon exercise of the
right of dissent will, subject to the provisions of the Section 302(b) of the
Internal Revenue Code, recognize gain or loss for Federal income tax purposes,
measured by the difference between the cost basis for his or her Shares and the
amount of payment received.
 
     PREFERRED SHAREHOLDERS WHO WISH TO RESERVE THE RIGHT TO EXERCISE
DISSENTERS' RIGHTS SHOULD REVIEW CAREFULLY THE FOREGOING DISCUSSION AND THE
PROVISIONS OF THE BUSINESS CORPORATION ACT SET FORTH IN ATTACHMENT A. THE
FAILURE TO COMPLY STRICTLY WITH THE DESCRIBED PROCEDURES WILL RESULT IN THE LOSS
OF ANY SUCH DISSENTERS' RIGHTS. ANY PREFERRED SHAREHOLDER WHO
                                       18
<PAGE>   19
 
CONTEMPLATES THE ASSERTION OF DISSENTERS' RIGHTS IS URGED TO CONSULT HIS OR HER
OWN COUNSEL.
 
PROXIES
 
     THE ENCLOSED PROXY (WHICH IS INCLUDED AS PART OF THE LETTER OF TRANSMITTAL
AND PROXY AND WHICH IS ALSO ENCLOSED SEPARATELY HEREWITH) IS SOLICITED BY IPC'S
BOARD, WHICH RECOMMENDS VOTING IN FAVOR OF THE PROPOSED AMENDMENT. ALL SHARES OF
IPC'S COMMON STOCK WILL BE VOTED IN FAVOR OF THE PROPOSED AMENDMENT. Shares of
IPC's cumulative preferred stock represented by properly executed proxies
received at or prior to the Special Meeting will be voted in accordance with the
instructions thereon. If no instructions are indicated, duly executed proxies
will be voted in accordance with the recommendation of the Board. It is not
anticipated that any other matters will be brought before the Special Meeting.
However, the enclosed proxy gives discretionary authority to the proxy holders
named therein should any other matters be presented at the Special Meeting, and
it is the intention of the proxy holders to act on any other matters in
accordance with their best judgment.
 
     Execution of a proxy will not prevent a shareholder from attending the
Special Meeting and voting in person. Any shareholder giving a proxy may revoke
it at any time before it is voted by delivering to the Secretary of IPC written
notice of revocation bearing a later date than the proxy, by delivering a duly
executed proxy bearing a later date, or by voting in person by ballot at the
Special Meeting. Withdrawal of Shares tendered pursuant to the Offer will not
revoke a properly executed proxy.
 
     IPC will bear the cost of the solicitation of proxies by the Board. IPC has
engaged MacKenzie Partners, Inc. to act as Information Agent in connection with
the solicitation of proxies for a fee of $       , plus reimbursement of
reasonable out-of-pocket expenses. Proxies will be solicited by mail, telephone
or other electronic means. In addition, officers and employees of IPC may also
solicit proxies personally or by telephone; such persons will receive no
additional compensation for these services. The Information Agent has not been
retained to make, and will not make, solicitations or recommendations in
connection with the Proposed Amendment. The Dealer Manager has not been retained
to act in any capacity in connection with the solicitation of proxies.
 
     IPC has requested that brokerage firms and other custodians, nominees and
fiduciaries forward solicitation materials to the beneficial owners of shares of
IPC's cumulative preferred stock held of record by such persons and will
reimburse such brokers and other fiduciaries for their reasonable out-of-pocket
expenses incurred in connection therewith.
 
SPECIAL CASH PAYMENTS
 
     Subject to the terms and conditions set forth in this Offer to Purchase and
Proxy Statement, if (but only if) the Proposed Amendment is adopted at the
Special Meeting, IPC will make a Special Cash Payment to each Preferred
Shareholder who voted at the Special Meeting in favor of the Proposed Amendment
either in person by ballot or by proxy, in the amount of $  for each Share held
by such Preferred Shareholder on the Record Date which is so voted, provided
that such Shares have not been tendered pursuant to the Offer. SPECIAL CASH
PAYMENTS WILL BE MADE TO PREFERRED SHAREHOLDERS AS OF THE RECORD DATE (IF SUCH
SHARES HAVE NOT BEEN TENDERED PURSUANT TO THE OFFER) ONLY IN RESPECT OF EACH
SHARE WHICH IS VOTED IN FAVOR OF THE PROPOSED AMENDMENT; PROVIDED, HOWEVER, THAT
THOSE PREFERRED SHAREHOLDERS WHO VALIDLY TENDER THEIR SHARES WILL BE ENTITLED
ONLY TO THE PURCHASE PRICE PER SHARE LISTED ON THE FRONT COVER OF THIS OFFER TO
PURCHASE AND PROXY STATEMENT. IPC has been advised that there is uncertainty
under state law, due to the lack of controlling precedent, as to the
permissibility of making Special Cash Payments. While IPC cannot predict how a
court would rule on the issue, IPC believes that ILN's Offer is fair to
Preferred Shareholders, that the Proposed Amendment is in the best interests of
IPC and its shareholders, and, accordingly, has decided to make the Special Cash
Payments. If the Proposed Amendment is adopted at the Special Meeting, Special
Cash Payments will be paid out of IPC's general funds, promptly after the
Proposed Amendment shall have become effective. However, no accrued interest
will be paid on the Special Cash Payments regardless of any delay in making such
payments.
 
                                       19
<PAGE>   20
 
     Only Preferred Shareholders on the Record Date (or their legal
representatives or attorneys-in-fact) are entitled to vote at the Special
Meeting and, if the Proposed Amendment is adopted at the Special Meeting, to
receive Special Cash Payments from IPC. Any beneficial holder of Shares who is
not the registered holder of such Shares as of the Record Date (as would be the
case for any beneficial holder whose Shares are registered in the name of such
holder's broker, dealer, commercial bank, trust company or other nominee) must
arrange with the record Preferred Shareholder to execute and deliver a proxy
form on such beneficial owner's behalf. If a beneficial holder of Shares intends
to attend the Special Meeting and vote in person, such beneficial holder must
obtain a legal proxy form from his or her broker, dealer, commercial bank, trust
company or other nominee.
 
     TO AVOID FEDERAL INCOME TAX BACKUP WITHHOLDING EQUAL TO 31% OF THE SPECIAL
CASH PAYMENT, EACH PREFERRED SHAREHOLDER VOTING IN FAVOR OF THE PROPOSED
AMENDMENT MUST NOTIFY THE DEPOSITARY OF SUCH PREFERRED SHAREHOLDER'S CORRECT
TAXPAYER IDENTIFICATION NUMBER AND PROVIDE CERTAIN OTHER INFORMATION BY PROPERLY
COMPLETING AND EXECUTING THE SUBSTITUTE FORM W-9 INCLUDED IN THE LETTER OF
TRANSMITTAL AND PROXY OR THE SUBSTITUTE FORM W-9 INCLUDED IN THE PROXY. FOREIGN
PREFERRED SHAREHOLDERS MUST SUBMIT A PROPERLY COMPLETED FORM W-8 IN ORDER TO
AVOID THE APPLICABLE BACKUP WITHHOLDING; PROVIDED, HOWEVER, THAT BACKUP
WITHHOLDING WILL NOT APPLY TO FOREIGN PREFERRED SHAREHOLDERS SUBJECT TO 30% (OR
LOWER TREATY RATE) WITHHOLDING ON SPECIAL CASH PAYMENTS. SEE "CERTAIN FEDERAL
INCOME TAX CONSEQUENCES."
 
SECURITY OWNERSHIP OF CERTAIN BENEFICIAL OWNERS AND MANAGEMENT
 
     IPC Securities. As noted above, ILN owns all the outstanding common stock
of IPC. ILN, IPC and their subsidiaries and affiliates do not beneficially own
any Shares as of January 31, 1998. None of the pension, profit sharing or other
retirement plans of such entities beneficially own any Shares as of January 31,
1998. In addition, IPC's and ILN's directors and executive officers do not
beneficially own any Shares as of January 31, 1998. There is no person or group
known by management of IPC to be the beneficial owner of more than 5% of the
Shares as of January 31, 1998.
 
     ILN Securities. The beneficial ownership of ILN's common stock held by each
director of ILN and IPC, the five most highly compensated executive officers of
ILN and IPC in 1997, and all directors and executive officers as a group of ILN
and IPC, as of January 31, 1998, is set forth in the following table.
 
<TABLE>
<CAPTION>
                                                              AMOUNT AND NATURE OF
                 NAME OF BENEFICIAL OWNER                    BENEFICIAL OWNERSHIP(1)   PERCENT OF CLASS
                 ------------------------                    -----------------------   ----------------
<S>                                                          <C>                       <C>
Larry F. Altenbaumer.......................................           13,092(2)               *
John G. Cook...............................................           11,894(2)               *
Larry D. Haab..............................................           68,250(2)               *
Paul L. Lang...............................................           21,216(2)               *
Robert A. Schultz..........................................            8,551(2)               *
J. Joe Adorjan.............................................                0                  *
C. Steven McMillan.........................................            1,300                  *
Robert M. Powers...........................................            8,550                  *
Sheli Z. Rosenberg.........................................                0                  *
Walter D. Scott............................................            5,150                  *
Joe J. Stewart.............................................                0                  *
Ronald L. Thompson.........................................            3,677                  *
Walter M. Vannoy...........................................            5,010                  *
Marilou von Ferstel........................................            4,420                  *
John D. Zeglis.............................................            2,626                  *
All directors and executive officers as a group............          187,021                  *
</TABLE>
 
- -------------------------
* Less than 1%.
 
                                       20
<PAGE>   21
 
(1) Each person named in the table has sole voting and investment power with
    respect to shares of ILN's common stock listed as owned by each person.
(2) Includes the following Shares issuable pursuant to stock options exercisable
    on or before March 31, 1998; Mr. Haab, 56,900; Mr. Lang, 17,800; Mr.
    Altenbaumer, 17,800; Mr. Cook, 9,900; and Mr. Schultz, 6,750.
 
BUSINESS TO COME BEFORE THE SPECIAL MEETING
 
     The following Proposed Amendment to the Articles is the only item of
business expected to be presented at the Special Meeting:
 
        To remove in its entirety ARTICLE V, Section 1, Clause (f)(1), limiting
        IPC's ability to issue or assume unsecured indebtedness (the "Debt
        Limitation Provision").
 
     THE FOLLOWING STATEMENTS, UNLESS THE CONTEXT OTHERWISE REQUIRES, ARE
SUMMARIES OF THE SUBSTANCE OR GENERAL EFFECT OF PROVISIONS OF THE ARTICLES, AND
ARE QUALIFIED IN THEIR ENTIRETY BY THE ARTICLES, INCLUDING ARTICLE V SECTION 1,
CLAUSE (F)(1) (AS DESCRIBED BELOW).
 
EXPLANATION OF THE PROPOSED AMENDMENT
 
     The Debt Limitation Provision in the Articles currently prohibits, without
the consent of the holders of a majority of the outstanding Shares, the issuance
or assumption by IPC of any unsecured notes, debentures or other securities
representing unsecured indebtedness (other than for the purpose of refunding
outstanding unsecured indebtedness or for the redemption or retirement of all
outstanding Shares) if, immediately after such issuance or assumption, the total
outstanding principal amount of all securities representing unsecured
indebtedness (including unsecured securities then to be issued or assumed) would
exceed 20% of the aggregate of (i) the total principal amount of all outstanding
secured indebtedness issued or assumed by IPC at the time of such issuance or
assumption and (ii) the capital and surplus of IPC, as then stated on IPC's
books of account. The Proposed Amendment, if adopted, would eliminate in its
entirety the Debt Limitation Provision, as set forth below, from the Articles:
 
          (f)(1) The Corporation shall not, without the consent (given by vote
     at a meeting called for that purpose) of the holders of at least a majority
     of the total number of shares of Preferred Stock then outstanding, issue
     any unsecured notes, debentures or other securities representing unsecured
     indebtedness, or assume any such unsecured indebtedness, for purposes other
     than (A) the refunding of outstanding unsecured indebtedness theretofore
     issued or assumed by the Corporation, (B) the reacquisition, redemption or
     other retirement of any indebtedness which reacquisition, redemption or
     other retirement has been approved by any regulatory authority having
     jurisdiction in the premises, or (C) the reacquisition, redemption or other
     retirement of all outstanding shares of Preferred Stock or of any other
     class of stock ranking prior to, or on a parity with, Preferred Stock as to
     dividends or other distributions, if immediately after such issue or
     assumption the total principal amount of all unsecured notes, debentures or
     other securities representing unsecured indebtedness issued or assumed by
     the Corporation including unsecured indebtedness then to be issued or
     assumed would exceed twenty percent (20%) of the aggregate of (a) the total
     principal amount of all bonds or other securities representing secured
     indebtedness issued or assumed by the Corporation and then to be
     outstanding, and (b) the capital and surplus of the Corporation as then to
     be stated on the books of account of the Corporation.
 
REASONS FOR THE PROPOSED AMENDMENT
 
     General. IPC believes that legislative, regulatory, technological and
market developments will lead to a more competitive environment in the electric
utility industry. As competition intensifies, flexibility and cost reduction
will be even more crucial to success. Because the electric utility industry is
extremely capital intensive, control and minimization of financing costs are of
particular importance. In response to the competitive forces and regulatory
changes faced by IPC, IPC has from time to time considered, and expects to
continue to consider, various strategies designed to enhance its competitive
position and to increase its ability to adapt to and anticipate changes in its
utility business.
                                       21
<PAGE>   22
 
     IPC believes that adoption of the Proposed Amendment is critical to
financial flexibility and capital cost reduction. If the Proposed Amendment is
adopted, the Debt Limitation Provision will be eliminated. Historically, IPC's
debt financing generally has been accomplished through the issuance of long-term
mortgage bonds, unsecured indebtedness and pollution control bonds. IPC has
mortgage bonds outstanding under two mortgages: (i) the 1943 Mortgage and Deed
of Trust, between IPC and Harris Trust and Savings Bank (the "1943 Mortgage"),
and (ii) the 1992 General Mortgage and Deed of Trust, between IPC and Harris
Trust and Savings Bank (the "1992 Mortgage"). Mortgage bonds issued under the
1943 Mortgage represent secured indebtedness placing a first priority lien on
substantially all of IPC's assets. While subject to the prior lien of the 1943
Mortgage, IPC's utility assets are also subject to the junior lien of the 1992
Mortgage. IPC's mortgage bonds issued under both the 1943 Mortgage and the 1992
Mortgage contain certain restrictive covenants with respect to, among other
things, the disposition of assets and the ability to issue additional mortgage
bonds. Unsecured indebtedness generally has fewer restrictions than mortgage
bonds. Short-term indebtedness, a lower cost form of debt available to IPC,
represents one type of unsecured indebtedness. Pollution control bond financing,
a more favorable type of financing due to its tax-exempt status, is available
only for very limited purposes.
 
     The Proposed Amendment will not only allow IPC to issue a greater amount of
unsecured indebtedness, but also will allow IPC to issue a greater amount of
total indebtedness. IPC, however, presently has no intention of issuing a
greater amount of unsecured debt or total debt than it would have issued absent
the adoption of the Proposed Amendment, except that (i) IPC may issue additional
unsecured debt in the event it determines to purchase the Shares from ILN and
(ii) IPC may issue debt in connection with a securitization financing authorized
under PA 90-561. Rather, it is IPC's intention to retain flexibility in the mix
of its outstanding debt and therefore have the option to use more short-term and
other unsecured debt and fewer mortgage bonds. In addition, as a regulated
utility, the issuance of any securities by IPC would continue to be subject to
the prior approval of the ICC (with respect to securities maturing in more than
one year) or the Federal Energy Regulatory Commission (with respect to
securities maturing in one year or less).
 
     Inasmuch as the Debt Limitation Provision contained in the Articles limits
IPC's flexibility in planning and financing its business activities, IPC
believes it ultimately will be at a competitive disadvantage if the Debt
Limitation Provision is not eliminated. The industry's new competitors (for
example, power marketers, exempt wholesale generators, independent power
producers and cogeneration facilities) generally are not subject to the type of
financing restrictions the Articles impose on IPC. Recently, several other
utilities with the same or similar charter restrictions have successfully
eliminated such provisions by soliciting their shareholders for the same or
similar amendments. In addition, some potential utility competitors have no
comparable provision restricting the issuance of unsecured debt. Given the onset
of competition in the utility industry, IPC must continue to explore new ways of
reducing costs and enhancing flexibility. IPC believes that the adoption of the
Proposed Amendment will be in the best long-term competitive interests of its
shareholders.
 
     Financial Flexibility. If the Proposed Amendment is adopted, IPC will have
increased flexibility (i) to choose among different types of debt financing and
(ii) to finance projects using the most cost effective means. IPC believes that
various types of unsecured debt alternatives may increase in importance as a
financing option. The availability and flexibility of unsecured debt is
necessary to take full advantage of changing conditions in securities markets.
 
     In addition, although IPC's earnings currently are sufficient to meet the
earnings coverage tests that must be satisfied before issuing additional
mortgage bonds and preferred stock, there is no guarantee that this will be true
in the future. Other utilities have been unable to issue mortgage bonds during
certain periods because of restrictive covenants in their mortgages. IPC's
inability to issue mortgage bonds or preferred stock in the future, combined
with the inability to issue additional unsecured debt, would limit IPC's
financing options to more costly options, including additional common equity.
Moreover, continued reliance on the issuance of mortgage bonds could limit IPC's
ability in the future to strategically redeploy its assets.
 
                                       22
<PAGE>   23
 
     Under the Debt Limitation Provision, IPC's use of unsecured short-term
indebtedness is presently restricted. However, IPC believes that the prudent use
of such indebtedness in excess of this provision is vital to effective financial
management of its business. Not only is unsecured short-term indebtedness
generally one of the least expensive forms of capital, it also provides
flexibility in meeting seasonal and business cycle fluctuations in cash
requirements, acts as a bridge between issues of permanent capital and can be
used when unfavorable conditions prevail in the market for long-term capital.
However, because of the Debt Limitation Provision, as of December 31, 1997, the
maximum amount of unsecured indebtedness that IPC would be authorized under its
Articles to issue or assume would be approximately $612.7 million. As of
December 31, 1997, IPC had approximately $444.8 million of unsecured
indebtedness outstanding, thus leaving an additional $167.9 million of capacity
available.
 
     Lower Costs. As previously mentioned, IPC's short-term debt issuances
generally represent one of its lowest-cost forms of financing. By increasing its
use of short-term debt, IPC may be able to lower its cost structure further,
thereby making its products more competitive and reducing its business risks.
However, with the Debt Limitation Provision in place, the availability and
corresponding benefits of short-term debt diminish. And although short-term debt
may expose the borrower to more volatility in interest rates, it should be noted
that the cost of short-term debt seldom exceeds the cost of other forms of
capital available at the same time.
 
     FOR ALL THE ABOVE REASONS, IPC'S BOARD BELIEVES THE BEST LONG-TERM
INTERESTS OF SHAREHOLDERS ARE SERVED BY, AND ENCOURAGES SHAREHOLDERS TO VOTE IN
FAVOR OF, THE ADOPTION OF THE PROPOSED AMENDMENT.
 
RELATIONSHIP WITH INDEPENDENT ACCOUNTANTS
 
     ILN's Board of Directors has selected Price Waterhouse LLP as independent
accountants for ILN and its subsidiaries, including IPC, for the year 1998. A
representative of Price Waterhouse LLP is expected to be present at the Special
Meeting with the opportunity to make a statement and to respond to appropriate
questions from shareholders.
 
                        PRICE RANGE OF SHARES; DIVIDENDS
 
     Shares of the 4.08% Series, 4.20% Series, 4.26% Series, 4.42% Series and
4.70% Series are listed and traded on the NYSE under the symbols "IPCprA,"
"IPCprB," "IPCprC," "IPCprD" and "IPCprE," respectively. The last reported sales
price on the NYSE, as of the close of business on [DAY BEFORE STATEMENT DATE],
for each of these Series of Preferred is shown on the front cover of this Offer
to Purchase and Proxy Statement.
 
     Shares of the 7.75% Series trade in the over-the-counter market under the
symbol "ILLNP". The last reported sales price in the over-the-counter market, as
of the close of business on [DAY BEFORE STATEMENT DATE], for the 7.75% Series of
Preferred is shown on the front cover of this Offer to Purchase and Proxy
Statement. However, Preferred Shareholders should be aware that there is no
established trading market for these Shares and that the Shares of the Series of
Preferred only trade sporadically and on a limited basis and, therefore, the
last reported sales price may not necessarily reflect the current market value
of such Shares.
 
     On                , 1998, there were issued and outstanding 283,290 shares
of the 4.08% Series of Preferred held by shareholders of record; 167,720 shares
of the 4.20% Series of Preferred held by shareholders of record; 136,000 shares
of the 4.26% Series of Preferred held by shareholders of record; 134,400 shares
of the 4.42% Series of Preferred held by shareholders of record; 176,000 shares
of the 4.70% Series of Preferred held by shareholders of record; and 241,700
shares of the 7.75% Series of Preferred held by shareholders of record.
 
     PREFERRED SHAREHOLDERS ARE URGED TO OBTAIN CURRENT MARKET QUOTATIONS, IF
AVAILABLE, FOR THE SHARES.
 
                                       23
<PAGE>   24
 
     The following table sets forth the high and low sales prices of each Series
of Preferred on the NYSE or in the over-the-counter market as reported by the
National Quotation Bureau, Inc., as applicable, and the cash dividends paid
thereon for the fiscal quarters indicated.
 
            DIVIDENDS AND PRICE RANGES OF CUMULATIVE PREFERRED STOCK
                          BY QUARTERS (1997 AND 1996)
 
<TABLE>
<CAPTION>
                                         1997 -- QUARTERS                                    1996 -- QUARTERS
                        --------------------------------------------------  --------------------------------------------------
                            1ST          2ND          3RD          4TH          1ST          2ND          3RD          4TH
                            ---          ---          ---          ---          ---          ---          ---          ---
<S>                     <C>          <C>          <C>          <C>          <C>          <C>          <C>          <C>
CUMULATIVE PREFERRED
  STOCK ($50 Par
  Value)
4.08% Series
  Dividends Paid Per
    Share.............     $0.51        $0.51        $0.51        $0.51        $0.51        $0.51        $0.51        $0.51
  Market Price -- $
    Per Share (NYSE)
    (High/Low)........  30.00/25.50  29.00/25.50  28.50/25.38  31.00/27.25  31.50/27.00  31.00/27.88  33.53/29.13  36.00/30.44
4.20% Series
  Dividends Paid Per
    Share.............   $0.52 1/2    $0.52 1/2    $0.52 1/2    $0.52 1/2    $0.52 1/2    $0.52 1/2    $0.52 1/2    $0.52 1/2
  Market Price -- $
    Per Share (NYSE)
    (High/Low)........  30.00/27.00  29.00/27.38  30.00/26.88  32.00/28.50  32.00/28.00  32.00/27.00  34.52/30.50  37.00/32.00
4.26% Series
  Dividends Paid Per
    Share.............   $0.53 1/4    $0.53 1/4    $0.53 1/4    $0.53 1/4    $0.53 1/4    $0.53 1/4    $0.53 1/4    $0.53 1/4
  Market Price -- $
    Per Share (NYSE)
    (High/Low)........  31.00/27.38  29.50/27.38  32.00/26.75  32.13/28.00  33.00/28.25  32.50/29.88  34.50/30.94  37.50/32.50
4.42% Series
  Dividends Paid Per
    Share.............   $0.55 1/4    $0.55 1/4    $0.55 1/4    $0.55 1/4    $0.55 1/4    $0.55 1/4    $0.55 1/4    $0.55 1/4
  Market Price -- $
    Per Share (NYSE)
    (High/Low)........  32.00/29.00  31.50/27.75  32.00/27.13  34.00/29.00  33.50/29.50  34.00/29.50  35.50/32.00  39.00/33.25
4.70% Series
  Dividends Paid Per
    Share.............   $0.58 3/4    $0.58 3/4    $0.58 3/4    $0.58 3/4    $0.58 3/4    $0.58 3/4    $0.58 3/4    $0.58 3/4
  Market Price -- $
    Per Share (NYSE)
    (High/Low)........  34.00/30.38  33.00/29.38  33.00/29.63  36.00/31.13  35.50/31.00  36.00/33.00  38.63/33.50  41.00/36.00
7.75% Series
  Dividends Paid Per
    Share.............   $0.96 7/8    $0.96 7/8    $0.96 7/8   $0.968 7/8    $0.96 7/8    $0.96 7/8    $0.96 7/8    $0.96 7/8
  Market Price -- $
    Per Share (OTC)
    (High/Low)........  52.50/52.50  51.75/50.50  53.13/53.13  54.50/52.50  48.25/47.50  50.63/48.50  52.63/52.63  52.50/52.50
</TABLE>
 
- -------------------------
NYSE -- New York Stock Exchange
 
OTC -- Over-the-Counter market quotations provided by National Quotation Bureau,
Inc. High and low bid quotations are not available for the 7.75% Series.
 
     Dividends for a Series of Preferred are payable when, as and if declared by
IPC's Board of Directors at the rate per annum included in such title of the
Series of Preferred listed on the front cover of this Offer to Purchase and
Proxy Statement. The May 1998 Dividend has been declared on each Series of
Preferred, payable May 1, 1998 to holders of record as of the close of business
on April 9, 1998. A tender and purchase of Shares pursuant to the Offer will not
deprive such Preferred Shareholder of his or her right to receive the May 1998
Dividend on his or her Shares, regardless of when such tender is made. Tendering
Preferred Shareholders will not be entitled to any dividends in respect of any
dividend period (or any portion thereof)
 
                                       24
<PAGE>   25
 
after May 1, 1998. The payment of the May 1998 Dividend will be made separately
from payments for Shares tendered in the Offer or the payment of any Special
Cash Payments.
 
                    CERTAIN FEDERAL INCOME TAX CONSEQUENCES
 
     In the opinion of Schiff Hardin & Waite, counsel to ILN and IPC, the
following summary describes the principal United States federal income tax
consequences of sales of Shares pursuant to the Offer and the receipt of Special
Cash Payments in connection with the adoption of the Proposed Amendment. This
summary is based on the Internal Revenue Code of 1986, as amended to the date
hereof (the "Code"), administrative pronouncements, judicial decisions and
existing and proposed Treasury Regulations, changes to any of which subsequent
to the date of this Offer to Purchase and Proxy Statement may adversely affect
the tax consequences described herein, possibly on a retroactive basis. This
summary is addressed to Preferred Shareholders who hold Shares as capital assets
within the meaning of Section 1221 of the Code. This summary does not discuss
all of the tax consequences that may be relevant to a Preferred Shareholder in
light of such Preferred Shareholder's particular circumstances or to Preferred
Shareholders subject to special rules (including certain financial institutions,
tax-exempt organizations, insurance companies, dealers in securities or
currencies, and Preferred Shareholders who are not citizens or residents of the
United States). Preferred Shareholders should consult their tax advisors with
regard to the application of the United States federal income tax laws to their
particular situations as well as any tax consequences arising under the laws of
any state, local or foreign taxing jurisdiction.
 
     As used herein, the term "United States Holder" means an owner of a Share
that is (i) for United States federal income tax purposes a citizen or resident
of the United States; (ii) a corporation, partnership or other entity created or
organized in or under the laws of the United States or of any political
subdivision thereof; (iii) an estate, or for taxable years beginning on or
before December 31, 1996, in general, any trust, the income of which is subject
to United States federal income taxation regardless of its source; or (iv) for
taxable years beginning after December 31, 1996, any trust if a court within the
United States is able to exercise primary supervision over the administration of
such trust and one or more United States fiduciaries have the authority to
control all substantial decisions of such trust. A "Non-United States Holder" is
a Preferred Shareholder that is not a United States Holder.
 
TAX CONSIDERATIONS FOR TENDERING PREFERRED SHAREHOLDERS
 
     Characterization of the Sale. A sale of Shares by a Preferred Shareholder
pursuant to the Offer will be a taxable transaction for Federal income tax
purposes.
 
     United States Holders. A United States Holder will recognize gain or loss
equal to the difference between the tax basis of such Holder's Shares and the
amount of cash received in exchange therefor. A United States Holder's gain or
loss will be long-term capital gain or loss if the holding period for the Shares
is more than one year as of the date of the sale of such Shares. The excess of
net long-term capital gains over net short-term capital losses is taxed at a
lower rate than ordinary income for certain non-corporate taxpayers. Capital
gain on Shares held by non-corporate taxpayers for more than eighteen months on
the date of the sale of such Shares will be subject to a reduced tax rate. The
distinction between capital gain or loss and ordinary income or loss is also
relevant for purposes of, among other things, limitations on the deductibility
of capital losses.
 
     Non-United States Holders. Any gain realized upon the sale of Shares by a
Non-United States Holder pursuant to the Offer generally will not be subject to
United States Federal income tax unless (i) such gain is effectively connected
with a trade or business in the United States of the Non-United States Holder,
or (ii) in the case of a Non-United States Holder who is an individual, such
individual is present in the United States for 183 days or more in the taxable
year of such sale and certain other conditions are met.
 
     A Non-United States Holder described in clause (i) above will be taxed on
the net gain derived from the sale at regular graduated United States Federal
income tax rates. If a Non-United States Holder that is a foreign corporation
falls under clause (i) above, it may also be subject to an additional "branch
profits tax" at a 30% rate (or such lower rate as may be specified by an
applicable income tax treaty). Unless an applicable
 
                                       25
<PAGE>   26
 
tax treaty provides otherwise, an individual Non-United States Holder described
in clause (ii) above will be subject to a flat 30% tax on the gain derived from
the sale, which may be offset by United States capital losses (notwithstanding
the fact that the individual is not considered a resident of the United States).
 
TAX CONSIDERATIONS FOR NON-TENDERING PREFERRED SHAREHOLDERS
 
     Preferred Shareholders, whether or not they receive Special Cash Payments,
will not recognize any taxable gain or loss with respect to the Shares as a
result of the modification of the Articles by the Proposed Amendment.
 
     United States Holders. There is no direct authority concerning the Federal
income tax consequences of the receipt of Special Cash Payments. IPC will, for
information reporting purposes, treat Special Cash Payments as ordinary
non-dividend income to recipient United States Holders.
 
     Non-United States Holders. IPC will treat Special Cash Payments paid to a
Non-United States Holder of Shares as subject to withholding of United States
Federal income tax at a 30% rate. However, Special Cash Payments that are
effectively connected with the conduct of a trade or business by the Non-United
States Holder within the United States are not subject to the withholding tax
(provided such Non-United States Holder provides two originals of Internal
Revenue Service ("IRS") Form 4224 stating that such Special Cash Payments are so
effectively connected), but instead are subject to United States Federal income
tax on a net income basis at applicable graduated individual or corporate rates.
Any such effectively connected Special Cash Payments received by a foreign
corporation may, under certain circumstances, be subject to an additional
"branch profits tax" at a 30% rate (or such lower rate as may be specified by an
applicable income tax treaty). A Non-United States Holder of Shares eligible for
a reduced rate of United States withholding tax pursuant to an income tax treaty
may obtain a refund of any excess amounts withheld by filing an appropriate
claim for refund with the IRS.
 
BACKUP WITHHOLDING
 
     ANY TENDERING PREFERRED SHAREHOLDER OR PREFERRED SHAREHOLDER WHO VOTES IN
FAVOR OF THE PROPOSED AMENDMENT BUT DOES NOT TENDER WHO FAILS TO COMPLETE AND
SIGN THE SUBSTITUTE FORM W-9 THAT IS INCLUDED IN THE APPLICABLE LETTER OF
TRANSMITTAL AND PROXY (OR, IN THE CASE OF A FOREIGN PREFERRED SHAREHOLDER, FORM
W-8 OBTAINABLE FROM THE DEPOSITARY) MAY BE SUBJECT TO A REQUIRED FEDERAL INCOME
TAX BACKUP WITHHOLDING OF 31% OF (1) IN THE CASE OF A TENDERING PREFERRED
SHAREHOLDER, THE GROSS AMOUNT PAYABLE TO SUCH PREFERRED SHAREHOLDER IN EXCHANGE
FOR THE SHARES OR (2) IN THE CASE OF A NON-TENDERING PREFERRED SHAREHOLDER WHO
VOTES IN FAVOR OF THE PROPOSED AMENDMENT, THE SPECIAL CASH PAYMENT. To prevent
backup United States Federal income tax withholding with respect to the purchase
price of Shares purchased pursuant to the Offer or the Special Cash Payment, a
United States Holder must provide the Depositary with the Preferred
Shareholder's correct taxpayer identification number and certify that the
Preferred Shareholder is not subject to backup withholding of Federal income tax
by completing the Substitute Form W-9 included in the applicable Letter of
Transmittal and Proxy. Certain Preferred Shareholders (including, among others,
all corporations and certain foreign shareholders) are exempt from backup
withholding. For a corporate United States Holder to qualify for such exemption,
such Preferred Shareholder must provide the Depositary with a properly completed
and executed Substitute Form W-9 attesting to its exempt status. In order for a
foreign Preferred Shareholder to qualify as an exempt recipient, the foreign
holder must submit a Form W-8, Certificate of Foreign Status, signed under
penalties of perjury, attesting to that Preferred Shareholder's exempt status. A
copy of Form W-8 may be obtained from the Depositary.
 
     Unless a Preferred Shareholder provides the appropriate certification,
under the applicable law and regulations concerning "backup withholding" of
Federal United States income tax, the Depositary will be required to withhold,
and will withhold, 31% of the gross proceeds otherwise payable to such Preferred
Shareholder or other payee. The amount of any backup withholding from a payment
to a Preferred
 
                                       26
<PAGE>   27
 
Shareholder will be allowed as a credit against such Preferred Shareholder's
United States federal income tax liability and may entitle such Preferred
Shareholder to a refund, provided that the required information is furnished to
the IRS. However, backup withholding is not required for amounts subject to
withholding discussed above under "Tax Consideration for Tendering Preferred
Shareholders -- Non-United States Holders" and "Tax Considerations for
Non-Tendering Preferred Shareholders -- Non-United States Holders."
 
                           SOURCE AND AMOUNT OF FUNDS
 
     Assuming that ILN purchases all outstanding Shares pursuant to the Offer,
the total amount required by ILN to purchase such Shares will be approximately
$  million, exclusive of the May 1, 1998 Dividend, fees and other expenses. ILN
intends to fund the Offer through borrowings under its $150 million Credit
Agreement, dated as of June 12, 1996, as amended on June 28, 1996, with various
financial institutions and CIBC Inc. as Administrative Agent (the "Credit
Agreement"). The Credit Agreement terminates, unless extended, on June 11, 1998.
The Credit Agreement permits ILN to borrow funds at floating interest rates
determined by reference to the federal funds rate published by the Federal
Reserve Bank of New York or, for certain fixed periods, at fixed interest rates
determined by the interbank Eurodollar market. ILN's borrowings under the Credit
Agreement are expected to be repaid through funds received from IPC, which
expects to derive its funds from internally generated funds or the issuance of
short-term debt.
 
               TRANSACTIONS AND AGREEMENTS CONCERNING THE SHARES
 
     Each of ILN and IPC has been advised by its directors and executive
officers that no directors or executive officers of the respective companies own
any Shares. Based upon the companies' records and upon information provided to
each company by its directors and executive officers, neither company nor, to
the knowledge of either, any of their subsidiaries, affiliates, directors or
executive officers, or associates of the foregoing, or any of their pension,
profit-sharing or retirement plans, has engaged in any transactions involving
Shares during the 60 business days preceding the date hereof. Neither company
nor, to the knowledge of either, any of its directors or executive officers or
an associate of the foregoing is a party to any contract, arrangement,
understanding or relationship relating directly or indirectly to the Offer with
any other person or entity with respect to any securities of IPC.
 
     IPC purchased Shares on the open market on the dates and at the prices
shown below in fiscal 1996 and 1997.
 
<TABLE>
<CAPTION>
                           NUMBER OF   RANGE OF PURCHASE PRICES   AVERAGE PURCHASE
SERIES    FISCAL QUARTER    SHARES            (HIGH/LOW)          PRICE PER SHARE
- ------    --------------   ---------   ------------------------   ----------------
<C>      <S>               <C>         <C>                        <C>
4.08%    3rd Quarter 1997    16,710        $36.520/$35.000            $35.606
4.20%    3rd Quarter 1997    12,280          37.590/34.841             35.762
4.26%    3rd Quarter 1997    14,000          36.059/36.059             36.059
4.42%    3rd Quarter 1997    15,600          37.413/37.413             37.413
4.70%    3rd Quarter 1997    24,000          38.989/38.989             38.989
7.75%    3rd Quarter 1996   135,100          52.750/52.125             52.421
</TABLE>
 
                  FEES AND EXPENSES ASSOCIATED WITH THE OFFER
 
     Dealer Manager, Depositary and Information Agent Fees. Donaldson, Lufkin &
Jenrette Securities Corporation will act as the Dealer Manager for ILN in
connection with the Offer. ILN has agreed to pay the Dealer Manager a fee of
$     per Share for any Shares tendered, accepted for payment and paid for
pursuant to the Offer and to pay the Dealer Manager a fee of $     per Share for
any Shares that are not tendered pursuant to the Offer but which vote in favor
of the Proposed Amendment, provided that the Proposed Amendment is adopted at
the Special Meeting. The Dealer Manager will also be reimbursed by ILN for its
reasonable out-of-pocket expenses, including attorneys' fees, and will be
indemnified against certain liabilities,
 
                                       27
<PAGE>   28
 
including certain liabilities under the federal securities laws, in connection
with the Offer. The Dealer Manager has rendered, is currently rendering and is
expected to continue to render various investment banking and other advisory
services to ILN and IPC. The Dealer Manager has received, and will continue to
receive, customary compensation from ILN and IPC for such services. ILN has
retained First Chicago Trust Company of New York as Depositary and MacKenzie
Partners, Inc. as Information Agent in connection with the Offer. The Depositary
and Information Agent will receive reasonable and customary compensation for
their services and will also be reimbursed for reasonable out-of-pocket
expenses, including attorney fees. ILN has agreed to indemnify the Depositary
and Information Agent against certain liabilities, including certain liabilities
under the federal securities law, in connection with the Offer. Neither the
Depositary nor the Information Agent has been retained to make solicitations or
recommendations in connection with the Offer.
 
     Solicited Tender Fees; Separate Fees. Pursuant to Instruction 10 of the
accompanying Letter of Transmittal and Proxy, ILN will pay a solicitation fee of
$     per Share that is tendered, accepted for payment and paid for pursuant to
the Offer in transactions for beneficial owners of fewer than           Shares
and a solicitation fee of $     per Share for transactions for beneficial owners
of           or more Shares; provided that solicitation fees payable in
transactions for beneficial owners of           or more Shares shall be paid 80%
to the Dealer Manager and 20% to any designated Soliciting Dealer (which may be
the Dealer Manager). If the Proposed Amendment is adopted at the Special
Meeting, IPC will pay to each designated Soliciting Dealer a separate fee of
$     per Share for Shares that are not tendered pursuant to the Offer but which
are voted in favor of the Proposed Amendment in transactions for beneficial
owners of fewer than           Shares and a separate fee of $     per Share for
Shares that are not tendered pursuant to the Offer but which are voted in favor
of the Proposed Amendment in transactions for beneficial owners of        or
more Shares; provided that the separate fee payable in transactions for
beneficial owners of           or more Shares shall be paid 80% to the Dealer
Manager and 20% to any designated Soliciting Dealer (which may be the Dealer
Manager). A designated Soliciting Dealer is an entity obtaining the tender or
proxy, if the Letter of Transmittal and Proxy or the separate Proxy, as the case
may be, shall include its name and it is (i) any broker or dealer in securities,
including a Dealer Manager in its capacity as a dealer or broker, which is a
member in good standing of any national securities exchange or of the NASD, (ii)
any foreign broker or dealer not eligible for membership in the NASD which
agrees to conform to the
NASD's Rules of Fair Practice in soliciting tenders outside the United States to
the same extent as though it were an NASD member, or (iii) any bank or trust
company.
 
     No solicitation fee or separate fee (other than solicitation fees payable
to the Dealer Manager as provided above) shall be payable to a Soliciting Dealer
with respect to the tender of Shares or the vote of Shares by a holder unless
the Letter of Transmittal and Proxy or the separate Proxy accompanying such
tender or vote, as the case may be, designates such Soliciting Dealer. No
solicitation fee or separate fee shall be payable to a Soliciting Dealer in
respect of Shares registered in the name of such Soliciting Dealer unless such
Shares are held by such Soliciting Dealer as nominee and such Shares are being
tendered or voted for the benefit of one or more beneficial owners identified on
the Letter of Transmittal and Proxy or on the Notice of Solicited Tenders. No
solicitation fee or separate fee shall be payable to a Soliciting Dealer if such
Soliciting Dealer is required for any reason to transfer the amount of such fee
to a depositing holder (other than itself). No solicitation fee shall be paid to
a Soliciting Dealer with respect to Shares tendered for such Soliciting Dealer's
own account and no separate fee shall be paid to a Soliciting Dealer with
respect to Shares voted for such Soliciting Dealer's own account. A Soliciting
Dealer shall not be entitled to a solicitation fee or a separate fee for Shares
beneficially owned by such Soliciting Dealer. No broker, dealer, bank, trust
company or fiduciary shall be deemed to be the agent of ILN, IPC, the
Depositary, the Dealer Manager or the Information Agent for purposes of the
Offer.
 
     Soliciting Dealers will include any of the organizations described in
clauses (i), (ii) and (iii) above even when the activities of such organizations
in connection with the Offer consist solely of forwarding to clients materials
relating to the Offer, including the Letter of Transmittal and Proxy and
tendering Shares as directed by beneficial owners thereof. No Soliciting Dealer
is required to make any recommendation to holders of Shares as to whether to
tender or refrain from tendering in the Offer. No assumption is made, in making
payment to any Soliciting Dealer, that its activities in connection with the
Offer included any activities other
 
                                       28
<PAGE>   29
 
than those described above, and for all purposes noted in all materials relating
to the Offer, the term "solicit" shall be deemed to mean no more than
"processing shares tendered" or "forwarding to customers materials regarding the
Offer."
 
     Stock Transfer Taxes. ILN will pay all stock transfer taxes, if any,
payable on account of the acquisition of Shares by ILN pursuant to the Offer,
except in certain circumstances where special payment or delivery procedures are
utilized pursuant to Instruction 6 of the accompanying Letter of Transmittal and
Proxy.
 
     Estimated Expenses. Assuming that all Shares of each Series of Preferred
are tendered and purchased by ILN pursuant to the Offer, it is estimated that
the expenses incurred by ILN in connection with the Offer will be as
approximately set forth below. ILN will be responsible for paying all such
expenses.
 
<TABLE>
<S>                                                             <C>
Dealer Manager Fees.........................................    $
Depositary and Information Agent Fees.......................    $
Solicitation Fees...........................................    $
Printing and Mailing Fees...................................    $
Filing Fees.................................................    $
Legal and Miscellaneous.....................................    $
                                                                -----------
     Total..................................................    $
                                                                ===========
</TABLE>
 
                   CERTAIN INFORMATION REGARDING ILN AND IPC;
                           INCORPORATION BY REFERENCE
 
     ILN is a holding company organized in Illinois in May 1994, which conducts
substantially all of its business through its subsidiaries. It has three
principal operating subsidiaries: IPC, organized in May 1923, is a combination
electric and gas utility; Illinova Generating Company, organized in October
1992, is an independent power company which invests in energy supply projects
and competes in the independent power market worldwide; and Illinova Energy
Partners, Inc., organized in July 1994, is in the business of (i) developing and
marketing energy-related services to the unregulated energy market in the United
States and (ii) brokering and marketing electric power and gas to various
customers. IPC's financial position and results of operations are currently the
principal factors affecting ILN's consolidated financial position and results of
operation.
 
     IPC is engaged in the generation, transmission, distribution and sale of
electric energy and the distribution, transportation and sale of natural gas in
the State of Illinois. Its service area is a widely diversified industrial and
agricultural area comprising approximately 15,000 square miles in northern,
central and southern Illinois. Electric service is provided at retail to 310
incorporated municipalities, adjacent suburban and rural areas and numerous
unincorporated municipalities. Gas service is provided to 257 incorporated
municipalities, adjacent suburban areas and numerous unincorporated
municipalities. The larger cities served include Decatur, East St. Louis (gas
only), Champaign, Danville, Belleville, Granite City, Bloomington (electric
only), Galesburg, Urbana and Normal (electric only).
 
     ILN and IPC are subject to the informational requirements of the Exchange
Act and in accordance therewith file reports and other information with the SEC.
Such reports and other information may be inspected and copied at the public
reference facilities maintained by the SEC at 450 Fifth Street, N.W.,
Washington, D.C. 20549; 500 West Madison Street, Suite 1400, Chicago, Illinois
60661-2511; and Seven World Trade Center, Suite 1300, New York, New York 10048.
Copies of such material can be obtained from the Public Reference Section of the
SEC, 450 Fifth Street, N.W., Washington D.C. 20549 at prescribed rates. The SEC
maintains a Web site at http://www.sec.gov containing reports, proxy and
information statements and other information regarding registrants that file
electronically with the SEC, including ILN and IPC. Reports, proxy materials and
other information about ILN and IPC are also available at the offices of the
NYSE, 20 Broad Street, New York, New York 10005. In connection with the Offer,
ILN has filed an Issuer Tender Offer Statement on Schedule 13E-4 and a Rule
13e-3 Transaction Statement on Schedule 13E-3 with the SEC that includes certain
additional information relating to the Offer. ILN's Schedule 13E-4 and
 
                                       29
<PAGE>   30
 
Schedule 13E-3 will not be available at the SEC's regional offices. IPC has
filed this Offer to Purchase and Proxy Statement (and related documents) with
the SEC pursuant to Rule 14a-6 of the Exchange Act.
 
                 SUMMARY OF CONSOLIDATED FINANCIAL INFORMATION;
                           INCORPORATION BY REFERENCE
 
     Set forth below is certain consolidated historical financial information of
IPC and its subsidiaries. The historical financial information (other than the
ratios of earnings to fixed charges) was derived from the audited consolidated
financial statements included in IPC's Annual Report on Form 10-K for the year
ended December 31, 1997.
 
CONDENSED INCOME STATEMENT DATA:
 
<TABLE>
<CAPTION>
                                                                YEAR ENDED DECEMBER 31,
                                                              ---------------------------
                                                                 1997             1996
                                                                 ----             ----
                                                              (THOUSANDS, EXCEPT RATIOS)
<S>                                                           <C>              <C>
Operating Revenues..........................................  $ 1,773.9        $ 1,688.7
Operating Income............................................      278.7            361.4
Allowance for Borrowed Funds Use During Construction........       (5.0)            (6.5)
Interest Expense............................................      128.7            133.0
Net Income (Loss)...........................................      (44.2)           228.6
  Less-Preferred Dividend Requirement.......................       21.5             22.3
  Plus -- Carrying Amount Over (Under) Consideration Paid
     for Redeemed Preferred Stock of Subsidiary.............        0.2             (0.7)
Net Income (Loss) Applicable to Common Stock................      (65.5)           205.6
Ratio of Earnings to Fixed Charges..........................        1.24             3.40
</TABLE>
 
                                       30
<PAGE>   31
 
CONDENSED BALANCE SHEET DATA (AT END OF PERIOD):
 
<TABLE>
<CAPTION>
                                                                   DECEMBER 31,
                                                              -----------------------
                                                                1997           1996
                                                                ----           ----
                                                                    (MILLIONS)
<S>                                                           <C>            <C>
Assets
  Plant and property........................................  $7,353.4       $6,981.5
  Less -- accumulated depreciation..........................   2,808.1        2,419.7
                                                              --------       --------
     Net utility plant......................................   4,545.3        4,561.8
  Nuclear fuel under capital lease..........................     133.0          101.7
  Investments and other assets..............................       5.9           14.5
  Current assets............................................     414.8          444.3
  Deferred charges..........................................     192.5          446.2
                                                              --------       --------
       Total................................................  $5,291.5       $5,568.5
                                                              ========       ========
Capital and Liabilities
  Common stock..............................................  $1,417.3       $1,416.4
  Treasury stock............................................    (207.7)         (86.2)
  Retained earnings.........................................      89.5          245.9
  Preferred stock...........................................      57.1           96.2
  Mandatorily redeemable preferred stock....................     197.0          197.0
  Long-term debt............................................   1,617.5        1,636.4
                                                              --------       --------
       Total capitalization.................................   3,170.7        3,505.7
  Current liabilities.......................................     729.1          655.5
  Deferred credits and other noncurrent liabilities.........   1,391.7        1,407.3
                                                              --------       --------
       Total................................................  $5,291.5       $5,568.5
                                                              ========       ========
</TABLE>
 
     The financial statements of IPC and related information included in its
Annual Report on Form 10-K for the year ended December 31, 1997, and its Current
Reports on Form 8-K, dated February 13, 1998 and January 21, 1998, each as filed
with the SEC, are hereby incorporated by reference. All documents subsequently
filed by IPC pursuant to Section 13(a), 13(c), 14 or 15(d) of the Exchange Act
after the date of this Offer to Purchase and Proxy Statement and prior to the
Expiration Date (or any extension thereof) shall be deemed to be incorporated by
reference in this Offer to Purchase and Proxy Statement and to be a part hereof
from the date of filing of such documents. Any statement contained in a document
incorporated or deemed to be incorporated by reference herein shall be deemed to
be modified or superseded for purposes of this Offer to Purchase and Proxy
Statement to the extent that a statement contained herein or in any other
subsequently filed documents which is deemed to be incorporated by reference
herein modifies or supersedes such statement. Any such statement so modified or
superseded shall not be deemed, except as so modified or superseded, to
constitute a part of this Offer to Purchase and Proxy Statement.
 
     IPC will provide without charge to each person to whom a copy of this Offer
to Purchase and Proxy Statement has been delivered, on the written or oral
request of any such person, a copy of any or all of the documents described
above which have been incorporated by reference in this Offer to Purchase and
Proxy Statement, other than exhibits to such documents. Written requests for
copies of such documents should be addressed to the Shareholder Services
Department, Illinova Corporation at 500 South 27th Street, Decatur, Illinois
62525 (telephone (800) 800-8220) or at its Website on the World Wide Web at
http://www.illinova.com. The information relating to ILN and IPC contained in
this Offer to Purchase and Proxy Statement does not purport to be comprehensive
and should be read together with the information contained in the documents
incorporated by reference.
 
                                       31
<PAGE>   32
 
                             SHAREHOLDER PROPOSALS
 
     If a shareholder intends to present a proposal at the 1999 Annual Meeting
of Shareholders of IPC, the proposal must be received by the Corporate Secretary
of IPC not later than November 12, 1998 for inclusion in IPC's proxy or
information statement and form of proxy, if applicable.
 
                                 MISCELLANEOUS
 
     The Offer is not being made to, nor will ILN accept tenders from, owners of
Shares in any jurisdiction in which the Offer or its acceptance would not be in
compliance with the laws of such jurisdiction. ILN is not aware of any
jurisdiction where the making of the Offer or the tender of Shares would not be
in compliance with applicable law. If ILN becomes aware of any jurisdiction
where the making of the Offer or the tender of Shares is not in compliance with
any applicable law, ILN will make a good faith effort to comply with such law.
If, after such good faith effort, ILN cannot comply with such law, the Offer
will not be made to (nor will tenders be accepted from or on behalf of) the
owners of Shares residing in such jurisdiction. In any jurisdiction in which the
securities, blue sky or other laws require the Offer to be made by a licensed
broker or dealer, the Offer will be deemed to be made on ILN's behalf by one or
more registered brokers or dealers licensed under the laws of such jurisdiction.
 
                                            ILLINOVA CORPORATION
                                            ILLINOIS POWER COMPANY
 
                    , 1998
 
                                       32
<PAGE>   33
 
                                                                    ATTACHMENT A
 
                          ILLINOIS DISSENTERS' RIGHTS
 
  SECTION 11.65. RIGHT TO DISSENT.
 
     (a) A shareholder of a corporation is entitled to dissent from, and obtain
payment for his or her shares in the event of any of the following corporate
actions:
 
          (1) consummation of a plan of merger or consolidation or a plan of
     share exchange to which the corporation is a party if
 
             (i) shareholder authorization is required for the merger or
        consolidation or the share exchange by Section 11.20 or the articles of
        incorporation or
 
             (ii) the corporation is a subsidiary that is merged with its parent
        or another subsidiary under Section 11.30;
 
          (2) consummation of sale, lease or exchange of all, or substantially
     all, of the property and assets of the corporation other than in the usual
     and regular course of business;
 
          (3) an amendment of the articles of incorporation that materially and
     adversely affects rights in respect of a dissenter's shares because it:
 
             (i) alters or abolishes a preferential right of such shares;
 
             (ii) alters or abolishes a right in respect of redemption,
        including a provision respecting a sinking fund for the redemption or
        repurchase, of such shares;
 
             (iii) in the case of a corporation incorporated prior to January 1,
        1982, limits or eliminates cumulative voting rights with respect to such
        shares; or
 
          (4) any other corporate action taken pursuant to a shareholder vote if
     the articles of incorporation, by-laws, or a resolution of the board of
     directors provide that shareholders are entitled to dissent and obtain
     payment for their shares in accordance with the procedures set forth in
     Section 11.70 or as may be otherwise provided in the articles, by-laws or
     resolution.
 
     (b) A shareholder entitled to dissent and obtain payment for his or her
shares under this Section may not challenge the corporate action creating his or
her entitlement unless the action is fraudulent with respect to the shareholder
or the corporation or constitutes a breach of a fiduciary duty owed to the
shareholder.
 
     (c) A record owner of shares may assert dissenters' rights as to fewer than
all the shares recorded in such person's name only if such person dissents with
respect to all shares beneficially owned by any one person and notifies the
corporation in writing of the name and address of each person on whose behalf
the record owner asserts dissenters' rights. The rights of a partial dissenter
are determined as if the shares as to which dissent is made and other shares
were recorded in the names of different shareholders. A beneficial owner of
shares who is not the record owner may assert dissenters' rights as to shares
held on such person's behalf only if the beneficial owner submits to the
corporation the record owner's written consent to the dissent before or at the
same time the beneficial owner asserts dissenters' rights.
 
  SECTION 11.70. PROCEDURE TO DISSENT.
 
     (a) If the corporate action giving rise to the right to dissent is to be
approved at a meeting of shareholders, the notice of meeting shall inform the
shareholders of their right to dissent and the procedure to dissent. If, prior
to the meeting, the corporation furnishes to the shareholders material
information with respect to the transaction that will objectively enable a
shareholder to vote on the transaction and to determine whether or not to
exercise dissenters' rights, a shareholder may assert dissenters' rights only if
the shareholder delivers to the corporation before the vote is taken a written
demand for payment for his or her shares if the proposed action is consummated,
and the shareholder does not vote in favor of the proposed action.
 
                                       A-1
<PAGE>   34
 
     (b) If the corporate action giving rise to the right to dissent is not to
be approved at a meeting of shareholders, the notice to shareholders describing
the action taken under Section 11.30 or Section 7.10 shall inform the
shareholders of their right to dissent and the procedure to dissent. If, prior
to or concurrently with the notice, the corporation furnishes to the
shareholders material information with respect to the transaction that will
objectively enable a shareholder to determine whether or not to exercise
dissenters' rights, a shareholder may assert dissenters' rights only if he or
she delivers to the corporation within 30 days from the date of mailing the
notice a written demand for payment for his or her shares.
 
     (c) Within 10 days after the date on which the corporate action giving rise
to the right to dissent is effective or 30 days after the shareholder delivers
to the corporation the written demand for payment, whichever is later, the
corporation shall send each shareholder who has delivered a written demand for
payment a statement setting forth the opinion of the corporation as to the
estimated fair value of the shares, the corporation's latest balance sheet as of
the end of a fiscal year ending not earlier than 16 months before the delivery
of the statement, together with the statement of income for that year and the
latest available interim financial statements, and either a commitment to pay
for the shares of the dissenting shareholder at the estimated fair value thereof
upon transmittal to the corporation of the certificate or certificates, or other
evidence of ownership, with respect to the shares, or instructions to the
dissenting shareholder to sell his or her shares within 10 days after delivery
of the corporation's statement to the shareholder. The corporation may instruct
the shareholder to sell only if there is public market for the shares at which
the shares may be readily sold. If the shareholder does not sell within that 10
day period after being so instructed by the corporation, for purposes of this
Section the shareholder shall be deemed to have sold his or her shares at the
average closing price of the shares, if listed on a national exchange, or the
average of the bid and asked price with respect to the shares quoted by a
principal market maker, if not listed on a national exchange, during that 10 day
period.
 
     (d) A shareholder who makes written demand for payment under this Section
retains all other rights of a shareholder until those rights are canceled or
modified by the consummation of the proposed corporate action. Upon consummation
of that action, the corporation shall pay to each dissenter who transmits to the
corporation the certificate or other evidence of ownership of the shares the
amount the corporation estimates to be the fair value of the shares, plus
accrued interest, accompanied by a written explanation of how the interest was
calculated.
 
     (e) If the shareholder does not agree with the opinion of the corporation
as to the estimated fair value of the shares or the amount of interest due, the
shareholder, within 30 days from the delivery of the corporation's statement of
value, shall notify the corporation in writing of the shareholder's estimated
fair value and amount of interest due and demand payment for the difference
between the shareholder's estimate of fair value and interest due and the amount
of the payment by the corporation or the proceeds of sale by the shareholder,
whichever is applicable because of the procedure for which the corporation opted
pursuant to subsection (c).
 
     (f) If, within 60 days from delivery to the corporation of the shareholder
notification of estimate of fair value of the shares and interest due, the
corporation and the dissenting shareholder have not agreed in writing upon the
fair value of the shares and interest due, the corporation shall either pay the
difference in value demanded by the shareholder, with interest, or file a
petition in the circuit court of the county in which either the registered
office or the principal office of the corporation is located, requesting the
court to determine the fair value of the shares and interest due. The
corporation shall make all dissenters, whether or not residents of this State,
whose demands remain unsettled parties to the proceeding as an action against
their shares and all parties shall be served with a copy of the petition.
Nonresidents may be served by registered or certified mail or by publication as
provided by law. Failure of the corporation to commence an action pursuant to
this Section shall not limit or affect the right of the dissenting shareholders
to otherwise commence an action as permitted by law.
 
     (g) The jurisdiction of the court in which the proceeding is commenced
under subsection (f) by a corporation is plenary and exclusive. The court may
appoint one or more persons as appraisers to receive evidence and recommend
decision of the question of fair value. The appraisers have the power described
in the order appointing them, or in any amendment to it.
 
                                       A-2
<PAGE>   35
 
     (h) Each dissenter made a party to the proceeding is entitled to judgment
for the amount, if any, by which the court finds that the fair value of his or
her shares, plus interest, exceeds the amount paid by the corporation or the
proceeds of sale by the shareholder, whichever amount is applicable.
 
     (i) The court, in a proceeding commenced under subsection (f), shall
determine all costs of the proceeding, including the reasonable compensation and
expenses of the appraisers, if any, appointed by the court under subsection (g),
but shall exclude the fees and expenses of counsel and experts for the
respective parties. If the fair value of the shares as determined by the court
materially exceeds the amount which the corporation estimated to be the fair
value of the shares or if no estimate was made in accordance with subsection
(c), then all or any part of the costs may be assessed against the corporation.
If the amount which any dissenter estimated to be the fair value of the shares
materially exceeds the fair value of the shares as determined by the court, then
all or any part of the costs may be assessed against that dissenter. The court
may also assess the fees and expenses of counsel and experts for the respective
parties, in amounts the court finds equitable, as follows:
 
          (1) Against the corporation and in favor of any or all dissenters if
     the court finds that the corporation did not substantially comply with the
     requirements of subsections (a), (b), (c), (d), or (f).
 
          (2) Against either the corporation or a dissenter and in favor of any
     other party if the court finds that the party against whom the fees and
     expenses are assessed acted arbitrarily, vexatiously, or not in good faith
     with respect to the rights provided by this Section.
 
     If the court finds that the services of counsel for any dissenter were of
substantial benefit to other dissenters similarly situated and that the fees for
those services should not be assessed against the corporation, the court may
award to that counsel reasonable fees to be paid out of the amounts awarded to
the dissenters who are benefitted. Except as otherwise provided in this Section,
the practice, procedure, judgment and costs shall be governed by the Code of
Civil Procedure.
 
     (j) As used in this Section:
 
          (1) "Fair value", with respect to a dissenter's shares, means the
     value of the shares immediately before the consummation of the corporate
     action to which the dissenter objects excluding any appreciation or
     depreciation in anticipation of the corporate action, unless exclusion
     would be inequitable.
 
          (2) "Interest" means interest from the effective date of the corporate
     action until the date of payment, at the average rate currently paid by the
     corporation on its principal bank loans or, if none, at a rate that is fair
     and equitable under all the circumstances.
 
                                       A-3
<PAGE>   36
 
     Facsimile copies of the Letter of Transmittal and Proxy will only be
accepted from Eligible Institutions. Facsimile copies of the separate Proxy will
be accepted from any holder. The Letter of Transmittal and Proxy and, if
applicable, certificates for Shares should be sent or delivered by each
tendering or voting Preferred Shareholder of IPC or his or her broker, dealer,
bank or trust company to the Depositary at one of its addresses set forth below.
 
                               The Depositary is:
 
                    FIRST CHICAGO TRUST COMPANY OF NEW YORK
 
<TABLE>
<CAPTION>
           By Mail:                           By Hand:                     By Overnight Courier:
           --------                           --------                     ---------------------
<S>                                <C>                                <C>
  First Chicago Trust Company        First Chicago Trust Company        First Chicago Trust Company
          of New York                        of New York                        of New York
   Attn: Tenders & Exchanges          Attn: Tenders & Exchanges          Attn: Tenders & Exchanges
         P.O. Box 2565                c/o The Depository Trust                Suite 4680-CBE
          Suite 4660                Company 55 Water Street, DTC              14 Wall Street
  Jersey City, NJ 07303-2565                     TAD                             8th Floor
                                   Vietnam Veterans Memorial Plaza          New York, NY 10005
                                         New York, NY 10041
</TABLE>
 
                                 By Facsimile:
 
                                 (201) 222-4720
                               or (201) 222-4721
 
                             Confirm by Telephone:
 
                                 (201) 222-4707
 
     Any questions or requests for assistance may be directed to the Information
Agent or the Dealer Manager at their respective telephone numbers and addresses
listed below. Requests for additional copies of this Offer to Purchase and Proxy
Statement, the Letter of Transmittal and Proxy, the separate Proxy or other
tender offer or proxy materials may be directed to the Information Agent, and
such copies will be furnished promptly at the companies' expense. Preferred
Shareholders may also contact their local broker, dealer, commercial bank or
trust company for assistance concerning the Offer.
 
                             The Information Agent:
 
                            MACKENZIE PARTNERS, INC.
                                156 Fifth Avenue
                            New York, New York 10010
                           (800) 322-2885 (Toll Free)
                         (212) 929-5500 (Call Collect)
 
                              The Dealer Manager:
 
                          DONALDSON, LUFKIN & JENRETTE
                             SECURITIES CORPORATION
                                277 Park Avenue
                            New York, New York 10172
                           (800) 334-1604 (Toll Free)
                         (212) 892-3351 (Call Collect)
                        Attn: Paul Galant or Jeff Dorst

<PAGE>   1
 
                                                                         IPC   %
 
                        LETTER OF TRANSMITTAL AND PROXY
                                  to Accompany
                Shares of    % Series Cumulative Preferred Stock
                          CUSIP Number 452092 ________
                                       of
                             ILLINOIS POWER COMPANY
              Tendered Pursuant to the Offer to Purchase for Cash
                                       by
                              ILLINOVA CORPORATION
                   dated [Statement Date], for Purchase at a
                       Purchase Price Of $      Per Share
 
       THE OFFER AND WITHDRAWAL RIGHTS WILL EXPIRE AT 5:00 P.M., NEW YORK
         CITY TIME, ON [EXPIRATION DATE], UNLESS THE OFFER IS EXTENDED.
 
                  To: First Chicago Trust Company of New York
 
<TABLE>
<CAPTION>
           By Mail:                         By Hand:                   By Overnight Courier:
           --------                         --------                   ---------------------
<S>                              <C>                              <C>
First Chicago Trust Company of   First Chicago Trust Company of   First Chicago Trust Company of
           New York                         New York                         New York
   Attn: Tenders & Exchanges        Attn: Tenders & Exchanges        Attn: Tenders & Exchanges
         P.O. Box 2565              c/o The Depository Trust              Suite 4680-CBE
          Suite 4660                         Company                      14 Wall Street
  Jersey City, NJ 07303-2565        55 Water Street, DTC TAD                 8th Floor
                                 Vietnam Veterans Memorial Plaza        New York, NY 10005
                                       New York, NY 10041
</TABLE>
 
  By Facsimile: (201) 222-4720 or 222-4721         Confirm by Telephone: (201)
                                                   222-4707
 
ILLINOVA CORPORATION ("ILN") WILL NOT BE REQUIRED TO ACCEPT FOR PAYMENT OR PAY
FOR ANY SHARES TENDERED IF THE PROPOSED AMENDMENT IS NOT APPROVED AND ADOPTED AT
THE SPECIAL MEETING. PREFERRED SHAREHOLDERS OF RECORD OF ILLINOIS POWER COMPANY
("IPC") HAVE THE RIGHT TO VOTE FOR THE PROPOSED AMENDMENT REGARDLESS OF WHETHER
THEY TENDER THEIR SHARES. IF THE PROPOSED AMENDMENT IS ADOPTED AT THE SPECIAL
MEETING, IPC WILL MAKE A SPECIAL CASH PAYMENT TO EACH PREFERRED SHAREHOLDER WHO
VOTED IN FAVOR OF THE PROPOSED AMENDMENT, PROVIDED THAT THEIR SHARES ARE NOT
TENDERED PURSUANT TO THE OFFER.
 
<TABLE>
<S>                                                          <C>              <C>              <C>
- ---------------------------------------------------------------------------------------------------------------
                                        DESCRIPTION OF SHARES TENDERED
- ---------------------------------------------------------------------------------------------------------------
      NAME(S) AND ADDRESS(ES) OF REGISTERED HOLDER(S)
 IF TENDERING SHARES, PLEASE FILL IN EXACTLY AS INFORMATION
APPEARS ON CERTIFICATE(S) (ATTACH ADDITIONAL SIGNED LIST IF    CERTIFICATE     REPRESENTED BY  NUMBER OF SHARES
                         NECESSARY)                             NUMBER(S)*     CERTIFICATE(S)     TENDERED**
- ---------------------------------------------------------------------------------------------------------------
                                                             ==================================================
                                                             --------------------------------------------------
- ---------------------------------------------------------------------------------------------------------------
                       TOTAL NUMBER OF SHARES TENDERED
- ---------------------------------------------------------------------------------------------------------------
   * Need not be completed by shareholders tendering by book-entry transfer.
  ** Unless otherwise indicated, it will be assumed that all Shares represented by any certificates delivered
     to the Depositary are being tendered. See Instruction 4.
- ---------------------------------------------------------------------------------------------------------------
</TABLE>
 
NOTE: IF YOU ARE VOTING AND TENDERING SHARES, USE THE PROXY CONTAINED IN THIS
LETTER OF TRANSMITTAL AND PROXY. IF YOU ARE VOTING BUT NOT TENDERING SHARES, USE
THE SEPARATE [PROXY CARD COLOR] PROXY.
<PAGE>   2
 
NOTE: IF SHARES ARE BEING TENDERED, THE REMAINDER OF THIS LETTER OF TRANSMITTAL
AND PROXY (THE "LETTER OF TRANSMITTAL AND PROXY") MUST BE COMPLETED, INCLUDING,
IF APPLICABLE, THE SUBSTITUTE FORM W-9 BELOW.
 
                                     PROXY
 
     The undersigned hereby appoints        ,        and        , or any of
them, as proxies, each with the power to appoint his substitute, and hereby
authorizes them to represent and to vote as designated hereunder and in their
discretion with respect to any other business properly brought before the
Special Meeting, all the shares of cumulative preferred stock of Illinois Power
Company ("IPC") which the undersigned is entitled to vote at the Special Meeting
of Shareholders to be held on           , 1998, or any adjournment(s) or
postponement(s) thereof.
 
DELIVERY OF THIS LETTER OF TRANSMITTAL AND PROXY TO AN ADDRESS OTHER THAN AS SET
FORTH ABOVE WILL NOT CONSTITUTE A VALID DELIVERY. YOU MUST SIGN THIS LETTER OF
TRANSMITTAL AND PROXY IN THE APPROPRIATE SPACE THEREFOR PROVIDED AND, IF YOU ARE
TENDERING ANY SHARES, COMPLETE THE SUBSTITUTE FORM W-9 SET FORTH BELOW OR A FORM
W-8, AS APPLICABLE. SEE INSTRUCTION 8 AND "IMPORTANT TAX INFORMATION" BELOW.
 
DO NOT SEND ANY CERTIFICATES TO DONALDSON, LUFKIN & JENRETTE SECURITIES
CORPORATION, MACKENZIE PARTNERS, INC., ILLINOVA CORPORATION OR ILLINOIS POWER
COMPANY.
 
THE INSTRUCTIONS ACCOMPANYING THIS LETTER OF TRANSMITTAL AND PROXY SHOULD BE
READ CAREFULLY BEFORE THIS LETTER OF TRANSMITTAL AND PROXY IS COMPLETED.
QUESTIONS REGARDING AND REQUESTS FOR COPIES OF THE OFFER TO PURCHASE AND PROXY
STATEMENT OR THIS LETTER OF TRANSMITTAL AND PROXY MAY BE DIRECTED TO MACKENZIE
PARTNERS, INC., THE INFORMATION AGENT, AT 156 FIFTH AVENUE, NEW YORK, NEW YORK
10010 OR TELEPHONE (800) 322-2885 (TOLL FREE).
 
This Letter of Transmittal and Proxy is to be used (a) if certificates are to be
forwarded to the First Chicago Trust Company of New York ("Depositary") or (b)
if delivery of tendered Shares (as defined below) is to be made by book-entry
transfer to the Depositary's account at The Depository Trust Company ("DTC" or
the "Book-Entry Transfer Facility") pursuant to the procedures set forth under
the heading "Terms of the Offer -- Procedure for Tendering Shares" in the Offer
to Purchase and Proxy Statement (as defined below).
 
Preferred Shareholders (as defined below) who wish to tender Shares but who
cannot deliver their Shares and all other documents required hereby to the
Depositary by the Expiration Date (as defined in the Offer to Purchase and Proxy
Statement) must tender their Shares pursuant to the guaranteed delivery
procedure set forth under the heading "Terms of the Offer -- Procedure for
Tendering Shares" in the Offer to Purchase and Proxy Statement. See Instruction
2. DELIVERY OF DOCUMENTS TO ILN, IPC OR THE BOOK-ENTRY TRANSFER FACILITY DOES
NOT CONSTITUTE A VALID DELIVERY.
 
If any of your certificate(s) for Shares have been lost, stolen or destroyed,
please call Illinova Corporation's Shareholder Services Department (800)
800-8220. In addition, you should advise the Shareholder Services Department of
any certificate(s) you have in your possession. You will need to complete an
Affidavit of Loss with respect to the lost certificate(s) (which will be
provided by the Shareholder Services Department) and pay an indemnity bond
premium fee.
 
     THIS LETTER OF TRANSMITTAL AND PROXY IS SOLICITED ON BEHALF OF THE BOARD OF
DIRECTORS OF IPC. The proxy contained herein, when properly executed, will be
voted in the manner directed herein by the undersigned shareholder(s). If no
direction is made, the proxy will be voted for Item 1.
<PAGE>   3
 
     INDICATE YOUR VOTE BY AN (X). THE BOARD OF DIRECTORS OF IPC RECOMMENDS
VOTING FOR ITEM 1.
 
ITEM 1.
 
     To remove in its entirety ARTICLE V, Section 1, Clause (f)(1) from the
Amended and Restated Articles of Incorporation of IPC (the "Articles"), which
limits IPC's ability to issue or assume unsecured indebtedness.
 
       [ ] FOR                   [ ] AGAINST                  [ ] ABSTAIN
 
NOTE: IF SHARES ARE BEING VOTED "FOR" THE PROPOSED AMENDMENT, THE SUBSTITUTE
FORM W-9 BELOW SHOULD BE COMPLETED TO AVOID BACK-UP WITHHOLDING ON THE SPECIAL
CASH PAYMENT.
 
     SHARES REPRESENTED BY ALL PROPERLY EXECUTED PROXIES WILL BE VOTED IN
ACCORDANCE WITH INSTRUCTIONS APPEARING ON THIS PROXY. IN THE ABSENCE OF SPECIFIC
INSTRUCTIONS, PROXIES WILL BE VOTED IN ACCORDANCE WITH THE RECOMMENDATIONS OF
THE BOARD OF DIRECTORS OF IPC AND IN THE DISCRETION OF THE PROXY HOLDERS AS TO
ANY OTHER MATTERS THAT MAY PROPERLY COME BEFORE THE SPECIAL MEETING.
 
     Any holder of Shares held of record on the Record Date in the name of
another holder must establish to the satisfaction of IPC his or her entitlement
to exercise or transfer this Proxy. This will ordinarily require an assignment
by such record holder in blank, or if not in blank, to and from each successive
transferee, including the holder, with each signature guaranteed by an Eligible
Institution. A form of irrevocable assignment of proxy has been provided herein.
 
Please check box if you plan to attend the Special Meeting.  [ ]
 
     (BOXES BELOW FOR USE BY ELIGIBLE INSTITUTIONS ONLY)
 
[ ]  CHECK HERE IF TENDERED SHARES ARE BEING DELIVERED BY BOOK-ENTRY TRANSFER TO
     THE DEPOSITARY'S ACCOUNT AT DTC AND COMPLETE THE FOLLOWING:
 
    Name of Tendering Institution:
 
    ----------------------------------------------------------------------------
    Account No.:
    ----------------------------------------------------------------------------
    VOI No.:
    ----------------------------------------------------------------------------
 
[ ]  CHECK HERE IF TENDERED SHARES ARE BEING DELIVERED PURSUANT TO A NOTICE OF
     GUARANTEED DELIVERY PREVIOUSLY SENT TO THE DEPOSITARY AND COMPLETE THE
     FOLLOWING:
 
    Name(s) of tendering shareholder(s):
                                        -------------------------------------
    Date of Execution of Notice of Guaranteed Delivery:
                                                       ----------------------
    Name of Institution that Guaranteed Delivery:
                                                 ----------------------------
    If delivery is by book-entry transfer:
    Name of Tendering Institution:
                                  -------------------------------------------
    Account No.:
                 ------------------------------------------------------------
    VOI No.:
             ----------------------------------------------------------------
<PAGE>   4
 
                    NOTE: SIGNATURES MUST BE PROVIDED BELOW
              PLEASE READ THE ACCOMPANYING INSTRUCTIONS CAREFULLY
 
Ladies and Gentlemen:
 
     The undersigned hereby tenders to Illinova Corporation, an Illinois
corporation ("ILN"), the shares in the amount set forth in the box above
designated "Description of Shares Tendered" pursuant to ILN's offer to purchase
any and all of the outstanding shares of the series of cumulative preferred
stock of Illinois Power Company, an Illinois corporation, and direct utility
subsidiary of ILN ("IPC"), shown on the first page hereof as to which this
Letter of Transmittal and Proxy is applicable (the "Shares") at the purchase
price per Share shown on the first page hereof, net to the seller in cash, upon
the terms and subject to the conditions set forth in the Offer to Purchase and
Proxy Statement, dated [STATEMENT DATE] (the "Offer to Purchase and Proxy
Statement"), receipt of which is hereby acknowledged, and in this Letter of
Transmittal and Proxy (which as to the Shares, together with the Offer to
Purchase and Proxy Statement, constitutes the "Offer"). WHILE HOLDERS OF SHARES
("PREFERRED SHAREHOLDERS") WHO WISH TO TENDER THEIR SHARES PURSUANT TO THE OFFER
NEED NOT VOTE IN FAVOR OF THE PROPOSED AMENDMENT TO IPC'S AMENDED AND RESTATED
ARTICLES OF INCORPORATION, AS SET FORTH IN THE OFFER TO PURCHASE AND PROXY
STATEMENT (THE "PROPOSED AMENDMENT"), THE OFFER IS CONDITIONED UPON THE PROPOSED
AMENDMENT BEING APPROVED AND ADOPTED AT THE SPECIAL MEETING (AS DEFINED IN THE
OFFER TO PURCHASE AND PROXY STATEMENT). See "Proposed Amendment and Proxy
Solicitation", "Terms of the Offer -- Extension of Tender Period; Termination;
Amendments" and "Terms of the Offer -- Certain Conditions of the Offer" in the
Offer to Purchase and Proxy Statement.
 
     Subject to, and effective upon, acceptance for payment of and payment for
the Shares tendered herewith in accordance with the terms and subject to the
conditions of the Offer (including, if the Offer is extended or amended, the
terms and conditions of any such extension or amendment), the undersigned hereby
sells, assigns and transfers to, or upon the order of, ILN all right, title and
interest in and to all the Shares that are being tendered hereby and hereby
constitutes and appoints First Chicago Trust Company of New York (the
"Depositary") the true and lawful agent and attorney-in-fact of the undersigned
with respect to such Shares, with full power of substitution (such power of
attorney being an irrevocable power coupled with an interest), to (a) deliver
certificates for such Shares, or transfer ownership of such Shares on the
account books maintained by DTC, together, in any such case, with all
accompanying evidences of transfer and authenticity, to or upon the order of
ILN, (b) present such Shares for registration and transfer on the books of IPC
and (c) receive all benefits and otherwise exercise all rights of beneficial
ownership of such Shares, all in accordance with the terms of the Offer. The
Depositary will act as agent for tendering shareholders for the purpose of
receiving payment from ILN and transmitting payment to tendering shareholders.
 
     The undersigned hereby represents and warrants that the undersigned has
full power and authority to tender, sell, assign and transfer the Shares
tendered hereby and that, when and to the extent the same are accepted for
payment by ILN, ILN will acquire good, marketable and unencumbered title
thereto, free and clear of all liens, restrictions, charges, encumbrances,
conditional sales agreements or other obligations relating to the sale or
transfer thereof, and the same will not be subject to any adverse claims. The
undersigned will, upon request, execute and deliver any additional documents
deemed by the Depositary or ILN to be necessary or desirable to complete the
sale, assignment and transfer of the Shares tendered hereby.
 
     All authority herein conferred or agreed to be conferred shall not be
affected by, and shall survive the death, bankruptcy or incapacity of the
undersigned, and any obligations of the undersigned hereunder shall be binding
upon the heirs, legal representatives, successors, assigns, executors and
administrators of the undersigned. Except as stated in the Offer, this tender is
irrevocable.
 
     The undersigned understands that tenders of Shares pursuant to any one of
the procedures described under the heading "Terms of the Offer -- Procedure for
Tendering Shares" in the Offer to Purchase and Proxy Statement and in the
instructions hereto will constitute the undersigned's acceptance of the terms
and conditions of the Offer, including the undersigned's representation and
warranty that (a) the undersigned has
<PAGE>   5
 
a net long position in the Shares being tendered within the meaning of Rule
14e-4 promulgated under the Securities Exchange Act of 1934, as amended, and (b)
the tender of such Shares complies with such Rule 14e-4. ILN's acceptance for
payment of Shares tendered pursuant to the Offer will constitute a binding
agreement between the undersigned and ILN upon the terms and subject to the
conditions of the Offer.
 
     The undersigned recognizes that, under certain circumstances set forth in
the Offer to Purchase and Proxy Statement, ILN may terminate or amend the Offer
or may not be required to purchase any of the Shares tendered hereby. In either
event, the undersigned understands that certificate(s) for any Shares not
tendered or not purchased will be returned to the undersigned.
 
     Unless otherwise indicated in the box below under the heading "Special
Payment Instructions", please issue the check for the purchase price of any
Shares purchased, and/or return any Shares not tendered or not purchased, in the
name(s) of the undersigned (and, in the case of Shares tendered by book-entry
transfer, by credit to the account at the Book-Entry Transfer Facility).
Similarly, unless otherwise indicated in the box below under the heading
"Special Delivery Instructions", please mail the check for the purchase price of
any Shares purchased and/or any certificates for Shares not tendered or not
purchased (and accompanying documents, as appropriate) to the undersigned at the
address shown below the undersigned signature(s). In the event that both
"Special Payment Instructions" and "Special Delivery Instructions are completed,
please issue the check for the purchase price of any Shares purchased and/or
return any Shares not tendered or not purchased in the name(s) of, and mail said
check and/or any certificates to, the person(s) so indicated. The undersigned
recognizes that ILN has no obligation, pursuant to the "Special Payment
Instructions", to transfer any Shares from the name of the registered holder(s)
thereof if ILN does not accept for payment any of the Shares so tendered.
 
                          SPECIAL PAYMENT INSTRUCTIONS
                        (SEE INSTRUCTIONS 1, 4, 5 AND 7)
To be completed ONLY if the check for the purchase price of Shares purchased
and/or certificates for Shares not tendered or not purchased are to be issued in
the name of someone other than the undersigned.
 
Issue: [ ] check to:
       [ ] certificate(s) to:
Name     
     ---------------------------------------------------------------------------
                                (Please Print)
 
Address
       -------------------------------------------------------------------------
 
- --------------------------------------------------------------------------------

- --------------------------------------------------------------------------------
                              (Include Zip Code)
                  
- --------------------------------------------------------------------------------
             (Taxpayer Identification or Social Security Number)
 




                         SPECIAL DELIVERY INSTRUCTIONS
                           (SEE INSTRUCTIONS 4 AND 7)
To be completed ONLY if the check for the purchase price of Shares purchased
and/or certificates for Shares not tendered or not purchased are to be mailed to
someone other than the undersigned or to the undersigned at an address other
than that shown below the undersigned's signature(s).
 
Mail: [ ] check to:
      [ ] certificate(s) to:
Name     
     ---------------------------------------------------------------------------
                                (Please Print)
 
Address
       -------------------------------------------------------------------------
 
- --------------------------------------------------------------------------------

- --------------------------------------------------------------------------------
                              (Include Zip Code)
                  
- --------------------------------------------------------------------------------
             (Taxpayer Identification or Social Security Number)
<PAGE>   6
 
- --------------------------------------------------------------------------------
 
                            SIGNATURE(S) OF OWNER(S)
 
   X
    --------------------------------------------------------------------------
 
   X
    --------------------------------------------------------------------------
 
   Dated:                                                               , 1998
         ---------------------------------------------------------------
 
   Name(s):
           ------------------------------------------------------------------
 
   --------------------------------------------------------------------------
                                (Please Print)
 
   Capacity (Full Title or "Individual," if applicable)
 
   --------------------------------------------------------------------------
 
   --------------------------------------------------------------------------
 
   Addresses:
             ----------------------------------------------------------------
 
   --------------------------------------------------------------------------
                               (Include Zip Code)
 
   Daytime Area Code and Telephone No.:
 
   --------------------------------------------------------------------------
 
        (Must be signed by the registered holder(s) exactly as name(s)
   appear(s) on the stock certificate(s) or on a security position listing or
   by person(s) authorized to become registered holder(s) by certificates and
   documents transmitted herewith. If signature is by a trustee, executor,
   administrator, guardian, attorney-in-fact, officer of a corporation or
   other person acting in a fiduciary or representative capacity, please set
   forth full title and see Instruction 5.)
 
              GUARANTEE OF SIGNATURE(S) (SEE INSTRUCTIONS 1 AND 5)
 
   Authorized Signature:
                        -----------------------------------------------------
 
   Name:
        ---------------------------------------------------------------------
 
   Name of Firm:
                -------------------------------------------------------------
 
   Address of Firm:
                   ----------------------------------------------------------
 
   Area Code and Telephone No.:
                               ----------------------------------------------
 
   Dated:                                                              , 1998
         --------------------------------------------------------------
 
   IF SHARES ARE BEING TENDERED, PLEASE COMPLETE SUBSTITUTE FORM W-9 BELOW
                        OR A FORM W-8, AS APPLICABLE.
- --------------------------------------------------------------------------------
<PAGE>   7
 
                               SOLICITED TENDERS
                              (SEE INSTRUCTION 10)
 
     As provided in Instruction 10, ILN will pay a solicitation fee of $
per Share that is tendered, accepted for payment and paid for pursuant to the
Offer in transactions for beneficial owners of fewer than      Shares and a
solicitation fee of $     per Share for transactions for beneficial owners of
     or more Shares; provided that solicitation fees payable in transactions for
beneficial owners of      or more Shares shall be paid 80% to the Dealer Manager
and 20% to any designated Soliciting Dealer (as defined in Instruction 10)
(which may be the Dealer Manager). However, Soliciting Dealers will not be
entitled to a solicitation fee for Shares beneficially owned by such Soliciting
Dealer.
 
     The above signed represents that the Soliciting Dealer which solicited and
obtained this tender is:
 
Name of Firm:
                                 (Please Print)
 
Name of Individual Broker or Financial Consultant:
                                 (Please Print)
 
Telephone Number of Broker or Financial Consultant:
 
Identification Number (if known):
 
Address:
 
                                  (Include zip code)
 
     The following to be completed ONLY if customer's Shares held in nominee
name are tendered.
 
<TABLE>
<S>                                                <C>
          NAME OF BENEFICIAL OWNER                          NUMBER OF SHARES TENDERED
</TABLE>
 
                     (ATTACH ADDITIONAL LIST IF NECESSARY)
 
     The acceptance of compensation by such Soliciting Dealer will constitute a
representation by it that (a) it has complied with the applicable requirements
of the Securities Exchange Act of 1934, as amended, and the applicable rules and
regulations thereunder, in connection with such solicitation; (b) it is entitled
to such compensation for such solicitation under the terms and conditions of the
Offer to Purchase and Proxy Statement; (c) in soliciting tenders of Shares, it
has used no solicitation materials other than those furnished by ILN; and (d) if
it is a foreign broker or dealer not eligible for membership in the National
Association of Securities Dealers, Inc. (the "NASD"), it has agreed to conform
to the NASD's Rules of Fair Practice in making solicitations.
 
     The payment of compensation to any Soliciting Dealer is dependent on such
Soliciting Dealer returning a Notice of Solicited Tenders to the Depositary.
 
     THIS LETTER OF TRANSMITTAL AND PROXY IS TO BE USED ONLY FOR THE TENDER OF
SHARES OF THE SERIES OF CUMULATIVE PREFERRED STOCK OF IPC SHOWN ON THE FIRST
PAGE HEREOF. ANY PERSON DESIRING TO TENDER SHARES OF ANY OTHER SERIES OF
CUMULATIVE PREFERRED STOCK FOR WHICH ILN IS MAKING A TENDER OFFER MUST SUBMIT
THE LETTER OF TRANSMITTAL AND PROXY RELATING TO THAT SPECIFIC SERIES.
<PAGE>   8
 
                                  INSTRUCTIONS
 
             FORMING PART OF THE TERMS AND CONDITIONS OF THE OFFER
 
     1. GUARANTEE OF SIGNATURES. Except as otherwise provided below, all
signatures on this Letter of Transmittal and Proxy must be guaranteed by a firm
that is a member in good standing of a registered national securities exchange
or the NASD or by a commercial bank or trust company having an office or
correspondent in the United States which is a participant in an approved
Medallion Signature Guarantee Program (each of the foregoing being referred to
as an "Eligible Institution"). Signatures on this Letter of Transmittal and
Proxy need not be guaranteed (a) if this Letter of Transmittal and Proxy is
signed by the registered holder(s) of the Shares (which term, for purposes of
this document, shall include any participant in one of the Book-Entry Transfer
Facilities whose name appears on a security position listing as the owner of
Shares) tendered herewith and such holder(s) has not completed the box above
under the heading "Special Payment Instructions" or the box above under the
heading "Special Delivery Instructions" on this Letter of Transmittal and Proxy,
or (b) if such Shares are tendered for the account of an Eligible Institution.
See Instruction 5.
 
     2. DELIVERY OF LETTER OF TRANSMITTAL AND PROXY AND SHARES. This Letter of
Transmittal and Proxy is to be used if (a) certificates are to be forwarded
herewith, or (b) delivery of Shares is to be made by book-entry transfer
pursuant to the procedures set forth under the heading "Terms of the Offer --
Procedure for Tendering Shares" in the Offer to Purchase and Proxy Statement.
Certificates for all physically delivered Shares, or a confirmation of a
book-entry transfer into the Depositary's account at the Book-Entry Transfer
Facility of all Shares delivered electronically, as well as a properly completed
and duly executed Letter of Transmittal and Proxy, and any other documents
required by this Letter of Transmittal and Proxy, must be received by the
Depositary at one of its addresses set forth on the front page of this Letter of
Transmittal and Proxy on or prior to the Expiration Date (as defined in the
Offer to Purchase and Proxy Statement) with respect to all Shares. Preferred
Shareholders who wish to tender their Shares yet who cannot deliver their Shares
and all other required documents to the Depositary on or prior to the Expiration
Date must tender their Shares pursuant to the guaranteed delivery procedure set
forth under the heading "Terms of the Offer -- Procedure for Tendering Shares --
Guaranteed Delivery Procedure" in the Offer to Purchase and Proxy Statement.
Pursuant to such procedure: (a) such tender must be made by or through an
Eligible Institution, (b) a properly completed and duly executed Notice of
Guaranteed Delivery in the form provided by ILN (with any required signature
guarantees) must be received by the Depositary on or prior to the applicable
Expiration Date and (c) the certificates for all physically delivered Shares, or
a confirmation of a book-entry transfer into the Depositary's account at the
Book-Entry Transfer Facility of all Shares delivered electronically, together
with a properly completed and duly executed Letter of Transmittal and Proxy and
any other documents required by this Letter of Transmittal and Proxy must be
received by the Depositary by 5:00 p.m. (New York City time) within three New
York Stock Exchange trading days after the date of execution of such Notice of
Guaranteed Delivery, all as provided under the heading "Terms of the Offer --
Procedure for Tendering Shares -- Guaranteed Delivery Procedure" in the Offer to
Purchase and Proxy Statement.
 
     THE METHOD OF DELIVERY OF SHARES AND ALL OTHER REQUIRED DOCUMENTS IS AT THE
OPTION AND RISK OF THE TENDERING PREFERRED SHAREHOLDER. IF CERTIFICATES FOR
SHARES ARE SENT BY MAIL, REGISTERED MAIL WITH RETURN RECEIPT REQUESTED, PROPERLY
INSURED, IS RECOMMENDED.
 
     No alternative, conditional or contingent tenders will be accepted. See
"Terms of the Offer -- Number of Shares; Purchase Prices; Expiration Date;
Dividends" in the Offer to Purchase and Proxy Statement. By executing this
Letter of Transmittal and Proxy, the tendering shareholder waives any right to
receive any notice of the acceptance for payment of the Shares.
 
     3. VOTING. WHILE PREFERRED SHAREHOLDERS WHO WISH TO TENDER THEIR SHARES
PURSUANT TO THE OFFER NEED NOT VOTE IN FAVOR OF THE PROPOSED AMENDMENT, THE
OFFER IS CONDITIONED UPON THE PROPOSED AMENDMENT BEING APPROVED AND ADOPTED AT
THE SPECIAL MEETING. In addition, Preferred Shareholders have the right to vote
for the Proposed Amendment regardless of whether they tender their Shares by
casting their vote and duly executing the proxy enclosed herewith or by voting
in person at the Special Meeting. By
<PAGE>   9
 
executing a Notice of Guaranteed Delivery, a Preferred Shareholder is deemed to
have tendered the Shares described in such Notice of Guaranteed Delivery and to
have voted such Shares in accordance with the proxy returned therewith, if any.
If no vote is indicated on an otherwise properly executed proxy, then all Shares
in respect of such proxy will be voted in favor of the Proposed Amendment. See
"Proposed Amendment and Proxy Solicitation" in the Offer to Purchase and Proxy
Statement. The Offer is being sent to all persons in whose names Shares are
registered on the books of IPC on the Record Date (as defined in the Offer to
Purchase and Proxy Statement) and transferees thereof. Only a record holder of
Shares on the Record Date may vote in person or by proxy at the Special Meeting.
No record date is fixed for determining which persons are permitted to tender
Shares. Any person who is the beneficial owner but not the record holder of
Shares must arrange for the record transfer of such Shares prior to tendering.
 
     4. PARTIAL TENDERS (NOT APPLICABLE TO SHAREHOLDERS WHO TENDER BY BOOK-ENTRY
TRANSFER). If fewer than all the Shares represented by any certificate delivered
to the Depositary are to be tendered, fill in the number of Shares that are to
be tendered in the box above under the heading "Description of Shares Tendered".
In such case, a new certificate for the remainder of the Shares represented by
the old certificate will be sent to the person(s) signing this Letter of
Transmittal and Proxy, unless otherwise provided in the box above under the
heading "Special Payment Instructions" or "Special Delivery Instructions", as
promptly as practicable following the expiration or termination of the Offer.
All Shares represented by certificates delivered to the Depositary will be
deemed to have been tendered unless otherwise indicated.
 
     5. SIGNATURES ON THIS LETTER OF TRANSMITTAL AND PROXY AND/OR NOTICE OF
GUARANTEED DELIVERY; STOCK POWERS AND ENDORSEMENTS. If either this Letter of
Transmittal and Proxy or the Notice of Guaranteed Delivery (together, the
"Tender Documents") is signed by the registered holder(s) of the Shares tendered
hereby, the signature(s) must correspond with the name(s) as written on the face
of the certificates without alteration, enlargement or any change whatsoever. If
any of the Shares tendered under either Tender Document is held of record by two
or more persons, all such persons must sign such Tender Document. If any of the
Shares tendered under either Tender Document is registered in different names or
different certificates, it will be necessary to complete, sign and submit as
many separate applicable Tender Documents as there are different registrations
or certificates. If either Tender Document is signed by the registered holder(s)
of the Shares tendered hereby, no endorsements of certificates or separate stock
powers are required unless payment of the purchase price is to be made to, or
Shares not tendered or not purchased are to be registered in the name of, any
person other than the registered holder(s). Signatures on any such certificates
or stock powers must be guaranteed by an Eligible Institution. See Instruction
1. If this Letter of Transmittal and Proxy is signed by a person other than the
registered holder(s) of the Shares tendered hereby, certificates must be
endorsed or accompanied by appropriate stock powers, in either case, signed
exactly as the name(s) of the registered holder(s) appear(s) on the certificates
for such Shares. Signature(s) on any such certificates or stock powers must be
guaranteed by an Eligible Institution. See Instruction 1. If either Tender
Document or any certificate or stock power is signed by a trustee, executor,
administrator, guardian, attorney-in-fact, officer of a corporation or other
person acting in a fiduciary or representative capacity, such person should so
indicate when signing, and proper evidence satisfactory to ILN of the authority
of such person so to act must be submitted.
 
     6. STOCK TRANSFER TAXES. Except as set forth in this Instruction 6, ILN
will pay or cause to be paid any stock transfer taxes with respect to the sale
and transfer of any Shares to it or its order pursuant to the Offer. If,
however, payment of the purchase price is to be made to, or Shares not tendered
or not purchased are to be registered in the name of, any person other than the
registered holder(s), or if tendered Shares are registered in the name of any
person other than the person(s) signing this Letter of Transmittal and Proxy,
the amount of any stock transfer taxes (whether imposed on the registered
holder(s), such other person or otherwise) payable on account of the transfer to
such person will be deducted from the purchase price unless satisfactory
evidence of the payment of such taxes, or exemption therefrom, is submitted. See
"Terms of the Offer -- Acceptance of Shares for Payment and Payment of Purchase
Price" in the Offer to Purchase and Proxy Statement. EXCEPT AS PROVIDED IN THIS
INSTRUCTION 6, IT WILL NOT BE NECESSARY TO AFFIX TRANSFER TAX STAMPS TO THE
CERTIFICATES REPRESENTING SHARES TENDERED HEREBY.
<PAGE>   10
 
     7. SPECIAL PAYMENT AND DELIVERY INSTRUCTIONS. If the check for the purchase
price of any Shares purchased is to be issued in the name of, and/or any Shares
not tendered or not purchased are to be returned to, a person other than the
person(s) signing this Letter of Transmittal and Proxy or if the check and/or
any certificate for Shares not tendered or not purchased are to be mailed to
someone other than the person(s) signing this Letter of Transmittal and Proxy or
to an address other than that shown in the box above under the heading "Name(s)
and Address(es) of Registered Holder(s)", then the "Special Payment
Instructions" and/or "Special Delivery Instructions" on this Letter of
Transmittal and Proxy should be completed. Preferred Shareholders tendering
Shares by book-entry transfer will have any Shares not accepted for payment
returned by crediting the account maintained by such Preferred Shareholder at
the Book-Entry Transfer Facility from which such transfer was made.
 
     8. SUBSTITUTE FORM W-9 AND FORM W-8. The tendering Preferred Shareholder is
required to provide the Depositary with either a correct Taxpayer Identification
Number ("TIN") on Substitute Form W-9, which is provided under "Important Tax
Information" below, or a properly completed Form W-8. Failure to provide the
information on either Substitute Form W-9 or Form W-8 may subject the tendering
Preferred Shareholder to a $50 penalty imposed by the Internal Revenue Service
and to 31% federal income tax backup withholding on the payment of the purchase
price for the Shares. The box in Part 2 of Substitute Form W-9 may be checked if
the tendering Preferred Shareholder has not been issued a TIN and has applied
for a number or intends to apply for a number in the near future. If the box in
Part 2 is checked and the Depositary is not provided with a TIN by the time of
payment, the Depositary will withhold 31% on all payments of the purchase price
for the Shares thereafter until a TIN is provided to the Depositary.
 
     9. REQUESTS FOR ASSISTANCE OR ADDITIONAL COPIES. Any questions or requests
for assistance may be directed to the Information Agent or the Dealer Manager at
their respective telephone numbers and addresses listed below. Requests for
additional copies of the Offer to Purchase and Proxy Statement, this Letter of
Transmittal and Proxy or other related tender offer materials may be directed to
the Information Agent and such copies will be furnished promptly at ILN's
expense. Preferred Shareholders may also contact their local broker, dealer,
commercial bank or trust company for assistance concerning the Offer.
 
     10. SOLICITED TENDERS. ILN will pay a solicitation fee of $     per Share
that is tendered, accepted for payment and paid for pursuant to the Offer in
transactions for beneficial owners of fewer than      Shares and a solicitation
fee of $     per Share for transactions for beneficial owners of      or more
Shares; provided that solicitation fees payable in transactions for beneficial
owners of      or more Shares shall be paid 80% to the Dealer Manager and 20% to
any designated Soliciting Dealer (which may be the Dealer Manager) covered by
the Letter of Transmittal and Proxy which designates, under the heading
"Solicited Tenders," as having solicited and obtained the tender, the name of
(a) any broker or dealer in securities, including a Dealer Manager in its
capacity as a dealer or broker, which is a member of any national securities
exchange or of the NASD, (b) any foreign broker or dealer not eligible for
membership in the NASD which agrees to conform to the NASD's Rules of Fair
Practice in soliciting tenders outside the United States to the same extent as
though it were an NASD member, or (c) any bank or trust company (each of which
is referred to herein as a "Soliciting Dealer"). No such fee shall be payable to
a Soliciting Dealer with respect to the tender of Shares by a holder unless the
Letter of Transmittal and Proxy accompanying such tender designates such
Soliciting Dealer. No such fee shall be payable to a Soliciting Dealer in
respect of Shares registered in the name of such Soliciting Dealer unless such
Shares are held by such Soliciting Dealer as nominee and such Shares are being
tendered for the benefit of one or more beneficial owners identified on the
Letter of Transmittal and Proxy or on the Notice of Solicited Tenders (included
in the materials provided to brokers and dealers). No such fee shall be payable
to a Soliciting Dealer with respect to the tender of Shares by the holder of
record, for the benefit of the beneficial owner, unless the beneficial owner has
designated such Soliciting Dealer. If tendered Shares are being delivered by
book-entry transfer, the Soliciting Dealer must return a Notice of Solicited
Tenders to the Depositary within three business days after expiration of the
Offer to receive a solicitation fee. No such fee shall be payable to a
Soliciting Dealer if such Soliciting Dealer is required for any reason to
transfer the amount of such fee to a depositing holder (other than itself). No
such fee shall be paid to a Soliciting Dealer with respect to Shares tendered
for such Soliciting Dealer's own account. No broker, dealer, bank, trust company
or fiduciary shall be deemed to be the agent of ILN, the Depositary, the
Information
<PAGE>   11
 
Agent or the Dealer Manager for purposes of the Offer. Soliciting Dealers will
include any organizations described in clauses (a), (b) or (c) above even when
the activities of such organization in connection with the Offer consist solely
of forwarding to clients materials relating to the Offer, including this Letter
of Transmittal and Proxy, and rendering Shares as directed by beneficial owners
thereof. No Soliciting Dealer is required to make any recommendation to holders
of Shares as to whether to tender or refrain from tendering in the Offer. No
assumption is made, in making payment to any Soliciting Dealer, that its
activities in connection with the Offer included any activities other than those
described above, and for all purposes noted in all materials relating to the
Offer, the term "solicit" shall be deemed to mean no more than "processing
shares tendered" or "forwarding to customers materials regarding the Offer."
 
     11. IRREGULARITIES. All questions as to the form of documents and the
validity, eligibility (including time of receipt) and acceptance of any tender
of Shares will be determined by ILN, in its sole discretion, and its
determination shall be final and binding. ILN reserves the absolute right to
reject any and all tenders of Shares that it determines are not in proper form
or the acceptance for payment of or payment for Shares that may, in the opinion
of ILN's counsel, be unlawful. ILN also reserves the absolute right to waive any
of the conditions to the Offer or any defect or irregularity in any tender of
Shares and ILN's interpretation of the terms and conditions of the Offer
(including these instructions) shall be final and binding. Unless waived, any
defects or irregularities in connection with tenders must be cured within such
time as ILN shall determine. None of ILN, IPC, the Dealer Manager, the
Depositary, the Information Agent or any other person shall be under any duty to
give notice of any defect or irregularity in tenders, nor shall any of them
incur any liability for failure to give any such notice. Tenders will not be
deemed to have been made until all defects and irregularities have been cured or
waived.
 
     12. LOST, DESTROYED OR STOLEN CERTIFICATES. If any of your certificate(s)
for Shares have been lost, stolen or destroyed, please call the ILN's
Shareholder Services Department at (800)800-8220. In addition, you should advise
ILN's Shareholder Services Department of any certificate(s) you have in your
possession. You will need to complete an Affidavit of Loss with respect to the
lost certificate(s) (which will be provided by ILN's Shareholder Services
Department) and pay an indemnity bond premium fee. The tender of Shares pursuant
to this Letter of Transmittal and Proxy will not be valid unless prior to the
Expiration Date: (a) such procedures have been completed and a replacement
certificate for the Shares has been delivered to the Depositary or (b) a Notice
of Guaranteed Delivery has been delivered to the Depositary. See Instruction 2.
 
     IMPORTANT: THIS LETTER OF TRANSMITTAL AND PROXY, DULY EXECUTED, TOGETHER
WITH, IF APPLICABLE, CERTIFICATES OR CONFIRMATION OF BOOK-ENTRY TRANSFER, AND
ALL OTHER REQUIRED DOCUMENTS MUST BE RECEIVED BY THE DEPOSITARY, OR, IF
APPLICABLE, THE NOTICE OF GUARANTEED DELIVERY MUST BE RECEIVED BY THE
DEPOSITARY, ON OR PRIOR TO THE EXPIRATION DATE.
 
                           IMPORTANT TAX INFORMATION
 
     Under United States Federal income tax law, a Preferred Shareholder whose
tendered Shares are accepted for payment is required to provide the Depositary
(as payer) with either such Preferred Shareholder's correct TIN on Substitute
Form W-9 or a properly completed Form W-8. If such Preferred Shareholder is an
individual, the TIN is his or her social security number. For businesses and
other entities, the number is the Federal employer identification number. If the
Depositary is not provided with the correct TIN or properly completed Form W-8,
the Preferred Shareholder may be subject to a $50 penalty imposed by the
Internal Revenue Code. In addition, payments that are made to such Preferred
Shareholder with respect to Shares purchased pursuant to the Offer may be
subject to 31% backup withholding. To avoid backup withholding, an individual
Preferred Shareholder is required to complete the Substitute Form W-9 attached
hereto certifying that the TIN provided on Substitute Form W-9 is correct and
that (a) the Preferred Shareholder has not been notified by the Internal Revenue
Service that he or she is subject to United States Federal income tax backup
withholding as a result of a failure to report all interest or dividends or (b)
the Internal Revenue Service has notified the Preferred Shareholder that he or
she is no longer subject to United
<PAGE>   12
 
States Federal income tax backup withholding. See the enclosed Guidelines for
Certification of Taxpayer Identification Number on Substitute Form W-9 for
additional instructions.
 
     Certain Preferred Shareholders (including, among others, all corporations
and certain foreign individuals) are exempt from backup withholding. For a
corporate United States Preferred Shareholder to qualify for such exemption,
such Preferred Shareholder must provide the Depositary with a properly completed
and executed Substitute Form W-9 attesting to its exempt status. In order for a
foreign Preferred Shareholder to qualify as an exempt recipient, such Preferred
Shareholder must submit to the Depositary a properly completed Internal Revenue
Service Form W-8, signed under penalties of perjury attesting to that Preferred
Shareholder's exempt status. A Form W-8 can be obtained from the Depositary.
 
     If United States Federal income tax backup withholding applies, the
Depositary is required to withhold 31% of any payments made to the Preferred
Shareholder. Backup withholding is not an additional tax. Rather, the United
States Federal income tax liability of persons subject to backup withholding
will be reduced by the amount of the tax withheld. If withholding results in an
overpayment of taxes, a refund may be obtained from the Internal Revenue
Service.
 
WHAT NUMBER TO GIVE THE DEPOSITARY
 
     The Preferred Shareholder is required to give the Depositary the social
security number or employer identification number of the registered owner of the
Shares. If the Shares are in more than one name or are not in the name of the
actual owner, consult the enclosed Guidelines for Certification of Taxpayer
Identification Number on Substitute Form W-9 for additional guidance on which
number to report.
<PAGE>   13
 
<TABLE>
<S>                          <C>                                                         <C>
- ------------------------------------------------------------------------------------------------------------------------
                                 PAYER'S NAME: FIRST CHICAGO TRUST COMPANY OF NEW YORK
- ------------------------------------------------------------------------------------------------------------------------
                               PART 1--PLEASE PROVIDE YOUR TIN IN THE BOX AT RIGHT AND
  SUBSTITUTE                   CERTIFY BY SIGNING AND DATING BELOW.                       -----------------------------
  FORM W-9                                                                                  Social Security Number(s)
                                                                                          OR --------------------------
                                                                                         Employer Identification Number
                             -------------------------------------------------------------------------------------------
 DEPARTMENT OF THE TREASURY    PART 2--                                                             PART 3--
 INTERNAL REVENUE SERVICE      CERTIFICATION -- Under Penalties of Perjury, I certify           Awaiting TIN  [ ]
                               that:
                               (1) The number shown on this form is my correct taxpayer
                                   identification number (or a TIN has not been issued
                                   to me but I have mailed or delivered an application
                                   to receive a TIN or intend to do so in the near
                                   future),
                               (2) I am not subject to backup withholding either
                               because (a) I have not been notified by the Internal
                                   Revenue Service (the "IRS") that I am subject to
                                   backup withholding as a result of a failure to
                                   report all interest or dividends, or (b) the IRS has
                                   notified me that I am no longer subject to backup
                                   withholding.
                             -------------------------------------------------------------------------------------------
                               You must cross out item (2) above if you have been notified by the IRS that you are
  PAYER'S REQUEST FOR          currently subject to backup withholding because of underreporting interest or dividends
  TAXPAYER IDENTIFICATION      on your tax return.
  NUMBER (TIN)                 SIGNATURE _________________________________  DATE  ____________________________  1998
- -----------------------------------------------------------------------------------------------------------------------
</TABLE>
 
NOTE: FAILURE TO COMPLETE AND RETURN THIS FORM MAY RESULT IN BACKUP WITHHOLDING
      OF 31% OF ANY PAYMENTS MADE TO YOU PURSUANT TO THE OFFER. PLEASE REVIEW
      THE ENCLOSED CERTIFICATION "GUIDELINES FOR CERTIFICATION OF TAXPAYER
      IDENTIFICATION NUMBER ON SUBSTITUTE FORM W-9" FOR ADDITIONAL DETAILS.
 
NOTE: YOU MUST COMPLETE THE FOLLOWING CERTIFICATE IF YOU CHECKED THE BOX IN PART
      2 OF SUBSTITUTE FORM W-9.
 
             CERTIFICATE OF AWAITING TAXPAYER IDENTIFICATION NUMBER
 
  I certify under penalties of perjury that a taxpayer identification number has
not been issued to me and either (1) I have mailed or delivered an application
to receive a taxpayer identification number to the appropriate Internal Revenue
Service Center or Social Security Administration Office or (2) I intend to do so
in the near future. I understand that if I do not provide a taxpayer
identification number by the time of payment, 31% of all payments of the
purchase price made to me will be withheld until I provide such a number.
 
SIGNATURE  __________________________________________________  DATE _______1998
<PAGE>   14
 
   The Information Agent for the Offer to Purchase and Proxy Solicitation is:
                            MACKENZIE PARTNERS, INC.
                                156 Fifth Avenue
                            New York, New York 10010
                           (800) 322-2885 (Toll Free)
                         (212) 929-5500 (Call Collect)
 
    The Dealer Manager for the Offer to Purchase and Proxy Solicitation is:
                          DONALDSON, LUFKIN & JENRETTE
                             SECURITIES CORPORATION
                                277 Park Avenue
                            New York, New York 10172
                           (800) 334-1604 (Toll Free)
                         (212) 892-3351 (Call Collect)
                        Attn: Paul Galant or Jeff Dorst

<PAGE>   1
 
              TO BE COMPLETED ONLY BY THOSE PREFERRED SHAREHOLDERS
                WHO ARE NOT TENDERING THEIR SHARES IN THE OFFER
 
                                     PROXY
 
     The undersigned hereby appoints        ,        and        , or any of
them, as proxies, each with the power to appoint his substitute, and hereby
authorizes them to represent and to vote as designated hereunder and in their
discretion with respect to any other business properly brought before the
Special Meeting, all the shares of cumulative preferred stock of Illinois Power
Company ("IPC") which the undersigned is entitled to vote at the Special Meeting
of Shareholders to be held on                , 1998, or any adjournment(s) or
postponement(s) thereof.
 
     THIS PROXY IS SOLICITED ON BEHALF OF THE BOARD OF DIRECTORS OF IPC. When
properly executed, this Proxy will be voted in the manner directed herein by the
undersigned shareholder(s). If no direction is made, the Proxy will be voted for
Item 1.
 
     INDICATE YOUR VOTE BY AN (X). THE BOARD OF DIRECTORS OF IPC RECOMMENDS
VOTING FOR ITEM 1.
 
ITEM 1.
 
     To remove in its entirety ARTICLE V, Section 1, Clause (f)(1) from the
Amended and Restated Articles of Incorporation of IPC (the "Articles"), which
limits IPC's ability to issue or assume unsecured indebtedness.
 
       [ ] FOR                   [ ] AGAINST                  [ ] ABSTAIN
 
NOTE: IF SHARES ARE BEING VOTED "FOR" THE PROPOSED AMENDMENT, THE SUBSTITUTE
FORM W-9 BELOW SHOULD BE COMPLETED TO AVOID BACK-UP WITHHOLDING ON THE SPECIAL
CASH PAYMENT.
 
     SHARES REPRESENTED BY ALL PROPERLY EXECUTED PROXIES WILL BE VOTED IN
ACCORDANCE WITH INSTRUCTIONS APPEARING ON THIS PROXY. IN THE ABSENCE OF SPECIFIC
INSTRUCTIONS, PROXIES WILL BE VOTED IN ACCORDANCE WITH THE RECOMMENDATIONS OF
THE BOARD OF DIRECTORS OF IPC AND IN THE DISCRETION OF THE PROXY HOLDERS AS TO
ANY OTHER MATTERS THAT MAY PROPERLY COME BEFORE THE SPECIAL MEETING.
 
     Any holder of Shares held of record on the Record Date in the name of
another holder must establish to the satisfaction of IPC his or her entitlement
to exercise or transfer this Proxy. This will ordinarily require an assignment
by such record holder in blank, or if not in blank, to and from each successive
transferee, including the holder, with each signature guaranteed by an Eligible
Institution.
 
Please check box if you plan to attend the Special Meeting. [ ]
 
                       Signature                        Date:             , 1998
                                --------------------         -------------
 
                       Print Name:
                                  ------------------
<PAGE>   2
 
                           NOTICE OF SOLICITED VOTES
 
     If the Proposed Amendment is adopted at the Special Meeting, IPC will pay
to each designated Soliciting Dealer a separate fee of $     per Share for
Shares that are not tendered pursuant to the Offer but which are voted in favor
of the Proposed Amendment in transactions for beneficial owners of fewer than
         Shares and a separate fee of $     per Share for Shares that are not
tendered pursuant to the Offer but which are voted in favor of the Proposed
Amendment in transactions for beneficial owners of      or more Shares;
provided that the separate fee payable in transactions for beneficial owners of
or more Shares shall be paid 80% to the Dealer Manager and 20% to any
designated Soliciting Dealer (which may be the Dealer Manager). However,
Soliciting Dealers will not be entitled to a fee for Shares beneficially owned
by such Soliciting Dealer. For purposes of this paragraph, a "Soliciting
Dealer" shall include: (a) any broker or dealer in securities, including a
Dealer Manager in its capacity as a dealer or broker, which is a member of any
national securities exchange or of the NASD, (b) any foreign broker or dealer
not eligible for membership in the NASD which agrees to conform to the NASD's
Rules of Fair Practice in soliciting votes outside the United States to the
same extent as though it were an NASD member, or (c) any bank or trust company.
No fee shall be payable to a Soliciting Dealer with respect to the vote of
Shares in favor of the Proposed Amendment by a holder unless the Proxy relating
to such Shares designates such Soliciting Dealer. No such fee shall be payable
to a Soliciting Dealer in respect of Shares registered in the name of such
Soliciting Dealer unless such Shares are held by such Soliciting Dealer as
nominee and such Shares are being voted for the benefit of one or more
beneficial owners identified on the Proxy. No such fee shall be payable to a
Soliciting Dealer with respect to the vote of Shares by the holder of record,
for the benefit of the beneficial owner, unless the beneficial owner has
designated such Soliciting Dealer in the Letter from the Dealer Manager to
Brokers, Dealers, Commercial Banks, Trust Companies and Other Nominees (the
"Broker Letter").
        
     The above signed represents that the Soliciting Dealer which solicited and
obtained this vote in favor of the Proposed Amendment is:
 
Name of Firm:
- --------------------------------------------------------------------------------
                                 (Please Print)
 
Name of Individual Broker
or Financial Consultant:
- --------------------------------------------------------------------------------
                                 (Please Print)
 
Telephone Number of Broker
or Financial Consultant:
- --------------------------------------------------------------------------------
 
Identification Number (if known):
- ---------------------------------------------------------------------------
 
Address:
- --------------------------------------------------------------------------------
                               (Include Zip Code)
 
     The following to be completed ONLY if customer's Shares held in nominee
name are tendered.
 
                            NAME OF BENEFICIAL OWNER
 
- ------------------------------------------------------
 
- ------------------------------------------------------
 
- ------------------------------------------------------
                         NUMBER OF SHARES VOTED FOR THE
                               PROPOSED AMENDMENT
 
- ------------------------------------------------------
 
- ------------------------------------------------------
 
- ------------------------------------------------------
 
                     (ATTACH ADDITIONAL LIST IF NECESSARY)
 
     The acceptance of compensation by such Soliciting Dealer will constitute a
representation by it that (a) it has complied with the applicable requirements
of the Securities Exchange Act of 1934, as amended, and the applicable rules and
regulations thereunder, in connection with such solicitation; (b) it is entitled
to such compensation for such solicitation under the terms and conditions of the
Offer to Purchase and Proxy
<PAGE>   3
 
Statement; (c) in soliciting votes in favor of the Proposed Amendment, it has
used no solicitation materials other than those furnished by IPC; and (d) if it
is a foreign broker or dealer not eligible for membership in the National
Association of Securities Dealers, Inc. (the "NASD"), it has agreed to conform
to the NASD's Rules of Fair Practice in making solicitations.
 
     The payment of compensation to any Soliciting Dealer is dependent on such
Soliciting Dealer returning a Notice of Solicited Votes to the Depositary.
<PAGE>   4
 
<TABLE>
<S>                          <C>                                                         <C>
- ----------------------------------------------------------------------------------------------------------------------------
                                 PAYER'S NAME: FIRST CHICAGO TRUST COMPANY OF NEW YORK
- ----------------------------------------------------------------------------------------------------------------------------
                               PART 1--PLEASE PROVIDE YOUR TIN IN THE BOX AT RIGHT AND
  SUBSTITUTE                   CERTIFY BY SIGNING AND DATING BELOW.                       ----------------------------------
  FORM W-9                                                                                   Social Security Number(s)

                                                                                          OR -------------------------------
                                                                                             Employer Identification Number
                             -----------------------------------------------------------------------------------------------
 DEPARTMENT OF THE TREASURY    PART 2--                                                   PART 3--
 INTERNAL REVENUE SERVICE      CERTIFICATION -- Under Penalties of Perjury, I certify     Awaiting TIN  [ ]
                               that:
                               (1) The number shown on this form is my correct taxpayer
                                   identification number (or a TIN has not been issued
                                   to me but I have mailed or delivered an application
                                   to receive a TIN or intend to do so in the near
                                   future),
                               (2) I am not subject to backup withholding either
                               because (a) I have not been notified by the Internal
                                   Revenue Service (the "IRS") that I am subject to
                                   backup withholding as a result of a failure to
                                   report all interest or dividends, or (b) the IRS has
                                   notified me that I am no longer subject to backup
                                   withholding.
                             ------------------------------------------------------------------------------------------------
                               You must cross out item (2) above if you have been notified by the IRS that you are
  PAYER'S REQUEST FOR          currently subject to backup withholding because of underreporting interest or dividends
  TAXPAYER IDENTIFICATION      on your tax return.
  NUMBER (TIN)                 SIGNATURE _________________________________  DATE  ____________________________  1998
- ----------------------------------------------------------------------------------------------------------------------------
</TABLE>
 

NOTE: FAILURE TO COMPLETE AND RETURN THIS FORM MAY RESULT IN BACKUP WITHHOLDING
      OF 31% OF ANY SPECIAL CASH PAYMENTS MADE TO YOU. PLEASE REVIEW THE
      ENCLOSED CERTIFICATION "GUIDELINES FOR CERTIFICATION OF TAXPAYER
      IDENTIFICATION NUMBER ON SUBSTITUTE FORM W-9" FOR ADDITIONAL DETAILS.
 
NOTE: YOU MUST COMPLETE THE FOLLOWING CERTIFICATE IF YOU CHECKED THE BOX IN PART
      2 OF SUBSTITUTE FORM W-9.
 
             CERTIFICATE OF AWAITING TAXPAYER IDENTIFICATION NUMBER
 
  I certify under penalties of perjury that a taxpayer identification number has
not been issued to me and either (1) I have mailed or delivered an application
to receive a taxpayer identification number to the appropriate Internal Revenue
Service Center or Social Security Administration Office or (2) I intend to do so
in the near future. I understand that if I do not provide a taxpayer
identification number by the time of payment, 31% of all payments of the
purchase price made to me will be withheld until I provide such a number.
 
SIGNATURE  __________________________________________________  DATE  1998


<PAGE>   1
 
                         NOTICE OF GUARANTEED DELIVERY
                                      FOR
 
                              ILLINOVA CORPORATION
                           OFFER TO PURCHASE FOR CASH
                         ANY AND ALL OUTSTANDING SHARES
            OF THE FOLLOWING SERIES OF CUMULATIVE PREFERRED STOCK OF
 
                             ILLINOIS POWER COMPANY
                  CUMULATIVE PREFERRED STOCK ($50 PAR VALUE):
                                  4.08% SERIES
                                  4.20% SERIES
                                  4.26% SERIES
                                  4.42% SERIES
                                  4.70% SERIES
                                  7.75% SERIES
 
     This form, or a form substantially equivalent to this form, must be used to
accept the Offer (as defined below) if certificates for shares of a series of
cumulative preferred stock (each a "Series of Preferred") of Illinois Power
Company ("IPC"), an Illinois corporation and direct utility subsidiary of
Illinova Corporation, an Illinois corporation ("ILN"), to be tendered pursuant
to the Offer (the "Shares") are not immediately available, if the procedure for
book-entry transfer cannot be completed on a timely basis, or if time will not
permit all other documents required by the Letter of Transmittal (as defined in
the Offer to Purchase and Proxy Statement, which is defined below) to be
delivered to the Depositary (as defined below) on or prior to the Expiration
Date (as defined in the Offer to Purchase and Proxy Statement). Such form may be
delivered by hand or transmitted by mail to the Depositary. See "Terms of the
Offer -- Procedure for Tendering Shares" in the Offer to Purchase and Proxy
Statement.
 
     A SEPARATE NOTICE OF GUARANTEED DELIVERY MUST BE USED FOR EACH SERIES OF
PREFERRED.
 
     THE ELIGIBLE INSTITUTION (AS DEFINED IN THE LETTER OF TRANSMITTAL AND
PROXY) WHICH COMPLETES THIS FORM MUST DELIVER THE LETTER OF TRANSMITTAL AND
PROXY AND CERTIFICATES FOR SHARES TO THE DEPOSITARY WITHIN THE TIME SHOWN
HEREIN. FAILURE TO DO SO COULD RESULT IN A FINANCIAL LOSS TO SUCH ELIGIBLE
INSTITUTION.
 
   To: First Chicago Trust Company of New York, Depositary (the "Depositary")
 
<TABLE>
<CAPTION>
           By Mail:                         By Hand:                   By Overnight Courier:
           --------                         --------                   ---------------------
<S>                              <C>                              <C>
First Chicago Trust Company of   First Chicago Trust Company of   First Chicago Trust Company of
           New York                         New York                         New York
   Attn: Tenders & Exchanges        Attn: Tenders & Exchanges        Attn: Tenders & Exchanges
         P.O. Box 2565              c/o The Depository Trust              Suite 4680-CBE
          Suite 4660                         Company                      14 Wall Street
  Jersey City, NJ 07303-2565        55 Water Street, DTC TAD                 8th Floor
                                 Vietnam Veterans Memorial Plaza        New York, NY 10005
                                       New York, NY 10041
</TABLE>
 
  By Facsimile: (201) 222-4720 or 222-4721         Confirm by Telephone: (201)
                                                   222-4707
 
     DELIVERY OF THIS INSTRUMENT TO AN ADDRESS OTHER THAN AS SET FORTH ABOVE
WILL NOT CONSTITUTE A VALID DELIVERY.
<PAGE>   2
 
     This form is not to be used to guarantee signatures. If a signature on a
Letter of Transmittal and Proxy is required to be guaranteed by an Eligible
Institution under the instructions thereto, such signature guarantee must appear
in the applicable space provided in the signature box on the Letter of
Transmittal and Proxy.
 
     The undersigned hereby tenders to ILN, upon the terms and subject to the
conditions set forth in the Offer to Purchase and Proxy Statement, dated
                    (the "Offer to Purchase and Proxy Statement"), and the
related Letter of Transmittal and Proxy (which together constitute the "Offer"),
receipt of which is hereby acknowledged, the number of Shares listed below,
pursuant to the guaranteed delivery procedure set forth in "Terms of the Offer
- -- Procedure for Tendering Shares" in the Offer to Purchase and Proxy Statement.
 
     WHILE PREFERRED SHAREHOLDERS WHO WISH TO TENDER THEIR SHARES PURSUANT TO
THE OFFER NEED NOT VOTE IN FAVOR OF THE PROPOSED AMENDMENT TO IPC'S AMENDED AND
RESTATED ARTICLES OF INCORPORATION, AS SET FORTH IN THE OFFER TO PURCHASE AND
PROXY STATEMENT (THE "PROPOSED AMENDMENT"), THE OFFER IS CONDITIONED UPON THE
PROPOSED AMENDMENT BEING APPROVED AND ADOPTED AT THE SPECIAL MEETING (AS DEFINED
IN THE OFFER TO PURCHASE AND PROXY STATEMENT). IN ADDITION, PREFERRED
SHAREHOLDERS OF RECORD HAVE THE RIGHT TO VOTE FOR THE PROPOSED AMENDMENT
REGARDLESS OF WHETHER THEY TENDER THEIR SHARES BY CASTING THEIR VOTE AND SIGNING
THE PROXY ENCLOSED HEREWITH (OR THE PROXY CONTAINED IN THE LETTER OF TRANSMITTAL
AND PROXY) OR BY VOTING IN PERSON AT THE SPECIAL MEETING. IF THE PROPOSED
AMENDMENT IS APPROVED AND ADOPTED BY IPC'S SHAREHOLDERS, IPC WILL MAKE A SPECIAL
CASH PAYMENT (AS DEFINED IN THE OFFER TO PURCHASE AND PROXY STATEMENT) TO EACH
PREFERRED SHAREHOLDER WHO VOTED IN FAVOR OF THE PROPOSED AMENDMENT, PROVIDED
THAT SUCH PREFERRED SHAREHOLDER'S SHARES ARE NOT TENDERED PURSUANT TO THE OFFER.
<PAGE>   3

<TABLE>
<S>                                                                     <C>      
 Series of Preferred                                                    Signature(s) of Holder(s):                            
 (Select One)                                                                                                                 
 [ ] 4.08% Series                                                       ----------------------------------------------------- 
 [ ] 4.20% Series                                                                                                             
 [ ] 4.26% Series                                                       ----------------------------------------------------- 
 [ ] 4.42% Series                                                                                                             
 [ ] 4.70% Series                                                       Name(s) of Holder(s):                                 
 [ ] 7.75% Series                                                                                                             
                                                                        ----------------------------------------------------- 
 Number of Shares:                                                                                                            
 --------------------------------                                       ----------------------------------------------------- 
                                                                                           (Please Type or Print)    
 Certificate Nos. (if available):                                                                                             
                                                                        Address and ZIP Code:                                 
 -----------------------------------------------------                                                                        
                                                                        ----------------------------------------------------- 
 -----------------------------------------------------                                                                        
                                                                        ----------------------------------------------------- 
 Check box if Shares will be delivered by                                                                                     
 book-entry transfer:                                                   Area Code and Telephone No.:                          
 [ ] The Depository Trust Company                                                                                             
                                                                        ----------------------------------------------------- 
                                                                                                                              
                                                                        Dated:                                                
                                                                              -----------------------------------------------
</TABLE>
 
                                   GUARANTEE
                    (NOT TO BE USED FOR SIGNATURE GUARANTEE)
 
      The undersigned, a firm that is a member of a registered national
 securities exchange or the National Association of Securities Dealers, Inc. or
 a commercial bank or trust company having an office or correspondent in the
 United States, guarantees (a) that the above-named person(s) has a net long
 position in the Shares being tendered within the meaning of Rule 14e-4
 promulgated under the Securities Exchange Act of 1934, as amended, (b) that
 such tender of Shares complies with such Rule 14e-4 and (c) to deliver to the
 Depositary at one of its addresses set forth above certificate(s) for the
 Shares tendered hereby, in proper form for transfer, or a confirmation of the
 book-entry transfer of the Shares tendered hereby into the Depositary's
 account at The Depository Trust Company together with a properly completed and
 duly executed Letter(s) of Transmittal and Proxy (or facsimile(s) thereof),
 with any required signature guarantee(s) and any other required documents, all
 within three New York Stock Exchange trading days after the date hereof.



<TABLE>
<S>                                                                     <C>
 
 -----------------------------------------------------                  -----------------------------------------------------
 Name of Firm                                                           Authorized Signature                                 
                                                                                                                             
 -----------------------------------------------------                  -----------------------------------------------------
 Address                                                                Name                                                 
                                                                                                                             
 -----------------------------------------------------                  -----------------------------------------------------
 City, State, Zip Code                                                  Title                                                
                                                                                                                             
 -----------------------------------------------------                  Dated:                                         , 1998
 Area Code and Telephone Number                                               -----------------------------------------

</TABLE>
 
DO NOT SEND STOCK CERTIFICATES WITH THIS FORM. YOUR STOCK CERTIFICATES MUST BE
SENT WITH THE APPLICABLE LETTER OF TRANSMITTAL AND PROXY.

<PAGE>   1
 
                         [ILLINOIS POWER COMPANY LOGO]
 
                             ILLINOIS POWER COMPANY
                             500 SOUTH 27TH STREET
                            DECATUR, ILLINOIS 62525
 
                   NOTICE OF SPECIAL MEETING OF SHAREHOLDERS
          TO BE HELD                     ,                     , 1998
 
TO SHAREHOLDERS OF
ILLINOIS POWER COMPANY
 
     NOTICE IS HEREBY GIVEN that a Special Meeting of Shareholders of Illinois
Power Company ("IPC") will be held at its principal office, 500 South 27th
Street, Decatur, Illinois 62525 on                     ,                     ,
1998 at 4:30 p.m., New York City time, for the following purposes:
 
        1. To approve an amendment to Illinois Power Company's Amended and
           Restated Articles of Incorporation to remove the limitation on the
           issuance or assumption of unsecured indebtedness; and
 
        2. To transact such other business as may properly come before the
           meeting or any adjournment thereof.
 
     The Board of Directors of IPC has fixed the close of business on
                    , 1998 as the record date for determining the shareholders
entitled to notice of, and to vote at, the meeting or any adjournment thereof.
 
     IT IS IMPORTANT THAT YOUR SHARES BE REPRESENTED AND VOTED AT THIS MEETING.
WHETHER OR NOT YOU EXPECT TO BE PRESENT AT THE MEETING, YOU ARE URGED TO SIGN
AND DATE THE ENCLOSED LETTER OF TRANSMITTAL AND PROXY AND/OR SEPARATE PROXY, AS
APPROPRIATE, AND RETURN IT IMMEDIATELY TO THE DEPOSITARY IN THE ACCOMPANYING
POSTAGE-PAID ENVELOPE. SEE THE OFFER TO PURCHASE AND PROXY STATEMENT ENCLOSED
HEREWITH FOR FURTHER INSTRUCTIONS.
 
     By order of the Board of Directors,
 
                                          ILLINOIS POWER COMPANY
 
                                          --------------------------------------
                                          By: Leah Manning Stetzner,
                                            General Counsel and Corporate
                                              Secretary

<PAGE>   1
 
              DONALDSON, LUFKIN & JENRETTE SECURITIES CORPORATION
 
                             THE DEALER MANAGER FOR
 
                              ILLINOVA CORPORATION
                           OFFER TO PURCHASE FOR CASH
           ANY AND ALL OUTSTANDING SHARES OF THE FOLLOWING SERIES OF
                         CUMULATIVE PREFERRED STOCK OF
 
                             ILLINOIS POWER COMPANY
 
283,290 SHARES, CUMULATIVE PREFERRED STOCK, 4.08% SERIES AT A PURCHASE PRICE OF
$  PER SHARE, CUSIP NUMBER 452092 20 8
167,720 SHARES, CUMULATIVE PREFERRED STOCK, 4.20% SERIES AT A PURCHASE PRICE OF
$  PER SHARE, CUSIP NUMBER 452092 30 7
136,000 SHARES, CUMULATIVE PREFERRED STOCK, 4.26% SERIES AT A PURCHASE PRICE OF
$  PER SHARE, CUSIP NUMBER 452092 40 6
134,400 SHARES, CUMULATIVE PREFERRED STOCK, 4.42% SERIES AT A PURCHASE PRICE OF
$  PER SHARE, CUSIP NUMBER 452092 50 5
176,000 SHARES, CUMULATIVE PREFERRED STOCK, 4.70% SERIES AT A PURCHASE PRICE OF
$  PER SHARE, CUSIP NUMBER 452092 60 4
241,700 SHARES, CUMULATIVE PREFERRED STOCK, 7.75% SERIES AT A PURCHASE PRICE OF
$  PER SHARE, CUSIP NUMBER 452092 79 4
 
THE OFFER AND WITHDRAWAL RIGHTS WILL EXPIRE AT 5:00 P.M., NEW YORK CITY TIME, ON
            , UNLESS EXTENDED.
 
                                                                [STATEMENT DATE]
 
To Brokers, Dealers, Commercial Banks,
  Trust Companies and Other Nominees:
 
     We have been appointed by Illinova Corporation, an Illinois corporation
("ILN"), to act as Dealer Manager and in connection therewith are enclosing the
material listed below relating to the invitation of ILN to the holders of each
series of cumulative preferred stock of Illinois Power Company, an Illinois
corporation and direct utility subsidiary of ILN ("IPC"), listed above (each a
"Series of Preferred") to tender any and all of their shares of a Series of
Preferred ("Shares") for purchase at the purchase price per Share listed above,
net to the seller in cash, upon the terms and subject to the conditions set
forth in the Offer to Purchase and Proxy Statement, dated [STATEMENT DATE] (the
"Offer to Purchase and Proxy Statement"), in the Proxy and in the Letter of
Transmittal and Proxy for the Shares tendered. As to each Series of Preferred,
the Offer to Purchase and Proxy Statement, together with the applicable Letter
of Transmittal and Proxy, constitutes the "Offer." ILN will purchase all Shares
validly tendered and not withdrawn, upon the terms and subject to the conditions
of the Offer. The Offer for a Series of Preferred is not conditioned upon any
minimum number of Shares of such Series of Preferred being tendered and is
independent of the Offer for any other Series of Preferred.
 
     WHILE PREFERRED SHAREHOLDERS WHO WISH TO TENDER THEIR SHARES PURSUANT TO
THE OFFER NEED NOT VOTE IN FAVOR OF THE PROPOSED AMENDMENT TO IPC'S AMENDED AND
RESTATED ARTICLES OF INCORPORATION, AS SET FORTH IN THE OFFER TO PURCHASE AND
PROXY STATEMENT (THE "PROPOSED AMENDMENT"), THE OFFER IS CONDITIONED UPON THE
PROPOSED AMENDMENT BEING ADOPTED AT THE SPECIAL MEETING (AS DEFINED IN THE OFFER
TO PURCHASE AND PROXY STATEMENT). IN ADDITION, PREFERRED SHAREHOLDERS OF RECORD
HAVE THE RIGHT TO
<PAGE>   2
 
VOTE FOR THE PROPOSED AMENDMENT REGARDLESS OF WHETHER THEY TENDER
THEIR SHARES BY CASTING THEIR VOTE AND SIGNING THE PROXY ENCLOSED HEREWITH, BY
CASTING THEIR VOTE AND SIGNING THE PROXY CONTAINED IN THE LETTER OF TRANSMITTAL
AND PROXY OR BY VOTING IN PERSON AT THE SPECIAL MEETING. IF THE PROPOSED
AMENDMENT IS ADOPTED BY IPC'S SHAREHOLDERS, IPC WILL MAKE A SPECIAL CASH PAYMENT
IN THE AMOUNT OF $     PER SHARE TO EACH PREFERRED SHAREHOLDER WHO VOTED IN
FAVOR OF THE PROPOSED AMENDMENT, PROVIDED THAT SUCH SHARES HAVE NOT BEEN
TENDERED PURSUANT TO THE OFFER. SEE "PROPOSED AMENDMENT AND PROXY SOLICITATION",
"TERMS OF THE OFFER -- CERTAIN CONDITIONS OF THE OFFER" AND "TERMS OF THE OFFER
- -- EXTENSION OF TENDER PERIOD; TERMINATION; AMENDMENTS" IN THE OFFER TO PURCHASE
AND PROXY STATEMENT.
 
     We are asking you to contact your clients for whom you hold Shares
registered in your name (or in the name of your nominee) or who hold Shares
registered in their own names. Please bring the Offer to their attention as
promptly as possible.
 
     ILN will pay a solicitation fee of $     per Share that is tendered,
accepted for payment and paid for pursuant to the Offer in transactions for
beneficial owners of fewer than      Shares and a solicitation fee of $     per
Share for transactions for beneficial owners of      or more Shares; provided
that solicitation fees payable in transactions for beneficial owners of      or
more Shares shall be paid 80% to the Dealer Manager and 20% to any designated
Soliciting Dealer (which may be the Dealer Manager). If the Proposed Amendment
is adopted at the Special Meeting, IPC will pay to each designated Soliciting
Dealer a separate fee of $     per Share for Shares that are not tendered
pursuant to the Offer but which are voted in favor of the Proposed Amendment in
transactions for beneficial owners of fewer than      Shares and a separate fee
of $     per Share for Shares that are not tendered pursuant to the Offer but
which are voted in favor of the Proposed Amendment in transactions for
beneficial owners of      or more Shares; provided that the separate fee payable
in transactions for beneficial owners of      or more Shares shall be paid 80%
to the Dealer Manager and 20% to any designated Soliciting Dealer (which may be
the Dealer Manager). A designated "Soliciting Dealer" is an entity obtaining the
tender or proxy, if the Letter of Transmittal and Proxy or the separate Proxy,
as the case may be, shall include its name and it is (i) any broker or dealer in
securities, including the Dealer Manager in their capacity as a broker or
dealer, which is a member in good standing of any national securities exchange
or of the National Association of Securities Dealers, Inc. (the "NASD"), (ii)
any foreign broker or dealer not eligible for membership in the NASD which
agrees to conform to the NASD's Rules of Fair Practice in soliciting tenders
outside the United States to the same extent as though it were an NASD member,
or (iii) any bank or trust company. No solicitation fee or separate fee (other
than solicitation fees payable to the Dealer Manager as provided above) shall be
payable to a Soliciting Dealer with respect to the tender of Shares or the vote
of Shares by a holder unless the Letter of Transmittal and Proxy or the separate
Proxy accompanying such tender or vote, as the case may be, designates such
Soliciting Dealer. No solicitation fee or separate fee shall be payable to a
Soliciting Dealer in respect of Shares registered in the name of such Soliciting
Dealer unless such Shares are held by such Soliciting Dealer as nominee and such
Shares are being tendered or voted for the benefit of one or more beneficial
owners identified on the Letter of Transmittal and Proxy or on the Notice of
Solicited Tenders (included below). No solicitation fee or separate fee shall be
payable to a Soliciting Dealer if such Soliciting Dealer is required for any
reason to transfer the amount of such fee to a depositing holder (other than
itself). No solicitation fee shall be paid to a Soliciting Dealer with respect
to Shares tendered for such Soliciting Dealer's own account and no separate fee
shall be paid to a Soliciting Dealer with respect to Shares voted for such
Soliciting Dealer's own account. A Soliciting Dealer shall not be entitled to a
solicitation fee or a separate fee for Shares beneficially owned by such
Soliciting Dealer. No broker, dealer, bank, trust company or fiduciary shall be
deemed to be the agent of ILN, IPC, the Depositary (as defined below), the
Dealer Manager or the Information Agent (as defined below) for purposes of the
Offer.
 
     Soliciting Dealers will include any of the organizations described in
clauses (i), (ii) and (iii) above even when the activities of such organizations
in connection with the Offer consist solely of forwarding to clients
<PAGE>   3
 
materials relating to the Offer, including the Letter of Transmittal and Proxy
and tendering Shares as directed by beneficial owners thereof. No Soliciting
Dealer is required to make any recommendation to holders of Shares as to whether
to tender or refrain from tendering in the Offer. No assumption is made, in
making payment to any Soliciting Dealer, that its activities in connection with
the Offer included any activities other than those described above, and for all
purposes noted in all materials relating to the Offer, the term "solicit" shall
be deemed to mean no more than "processing shares tendered" or "forwarding to
customers materials regarding the Offer."
 
     ILN will also, upon request, reimburse Soliciting Dealers for reasonable
and customary handling and mailing expenses incurred by them in forwarding
materials relating to the Offer to their customers. ILN will pay all stock
transfer taxes applicable to its purchase of Shares pursuant to the Offer,
subject to Instruction 6 of the Letter of Transmittal and Proxy.
 
     IN ORDER FOR A SOLICITING DEALER TO RECEIVE A SOLICITATION FEE OR A
SEPARATE FEE, FIRST CHICAGO TRUST COMPANY OF NEW YORK, AS DEPOSITARY (THE
"DEPOSITARY"), MUST HAVE RECEIVED FROM SUCH SOLICITING DEALER A PROPERLY
COMPLETED AND DULY EXECUTED NOTICE OF SOLICITED TENDERS AND PROXIES IN THE FORM
ATTACHED HERETO WITHIN THREE BUSINESS DAYS AFTER THE EXPIRATION OF THE OFFER OR
A PROPERLY EXECUTED PROXY ON OR BEFORE THE EXPIRATION DATE.
 
     For your information and for forwarding to your clients for whom you hold
Shares registered in your name (or in the name of your nominee), we are
enclosing the following documents:
 
     1. The Offer to Purchase and Proxy Statement, dated [STATEMENT DATE].
 
     2. A separate Letter of Transmittal and Proxy for each Series of Preferred
for your use and for the information of your clients.
 
     3. A separate Proxy for each Series of Preferred for your use and for the
information of your clients.
 
     4. A letter to shareholders of IPC from its Chairman of the Board and Chief
Executive Officer.
 
     5. A Notice of Guaranteed Delivery to be used to accept the Offer if the
Shares and all other required documents cannot be delivered to the Depositary by
the applicable Expiration Date (as defined in the Offer to Purchase and Proxy
Statement).
 
     6. A form of letter which may be sent to your clients for whose accounts
you hold Shares registered in your name or in the name of your nominee, with
space for obtaining such clients' instructions with regard to the Offer and with
regard to the Proxy solicitation by IPC.
 
     7. Guidelines of the Internal Revenue Service for Certification of Taxpayer
Identification Number on Substitute Form W-9, providing information relating to
backup federal income tax withholding.
 
     8. A return envelope addressed to First Chicago Trust Company of New York,
the Depositary.
 
     9. A Notice of Special Meeting of Shareholders.
 
     Each Series of Preferred has its own Letter of Transmittal and Proxy, and
only the applicable Letter of Transmittal and Proxy for a particular Series or a
Notice of Guaranteed Delivery may be used to tender Shares of such Series of
Preferred.
 
     We urge you to contact your clients as promptly as possible. Please note
that the Offer and withdrawal rights will expire at 5:00 p.m., New York City
time, on [EXPIRATION DATE], unless the Offer is extended.
 
     NEITHER ILN, IPC, THEIR RESPECTIVE BOARDS OF DIRECTORS NOR ANY OF THEIR
RESPECTIVE OFFICERS MAKES ANY RECOMMENDATION TO ANY PREFERRED SHAREHOLDER AS TO
WHETHER TO TENDER ANY OR ALL SHARES. EACH PREFERRED SHAREHOLDER MUST MAKE HIS OR
HER OWN DECISION AS TO WHETHER TO TENDER SHARES AND, IF SO, HOW MANY SHARES TO
TENDER.
<PAGE>   4
 
     Any questions or requests for assistance or additional copies of the
enclosed materials may be directed to MacKenzie Partners, Inc., the Information
Agent, or to us, as Dealer Manager, at the respective addresses and telephone
numbers set forth on the back cover of the enclosed Offer to Purchase and Proxy
Statement.
 
Very truly yours,
 
DONALDSON, LUFKIN & JENRETTE SECURITIES CORPORATION
 
     NOTHING CONTAINED HEREIN OR IN THE ENCLOSED DOCUMENTS SHALL CONSTITUTE YOU
OR ANY PERSON AS THE AGENT OF ILN, IPC, THE DEALER MANAGER, THE INFORMATION
AGENT OR THE DEPOSITARY, OR AUTHORIZE YOU OR ANY OTHER PERSON TO USE ANY
DOCUMENT OR MAKE ANY STATEMENT ON BEHALF OF ANY OF THEM IN CONNECTION WITH THE
OFFER OTHER THAN THE DOCUMENTS ENCLOSED HEREWITH AND THE STATEMENTS CONTAINED
THEREIN.
 
                    NOTICE OF SOLICITED TENDERS AND PROXIES
                   FOR THE CUMULATIVE PREFERRED STOCK OF IPC
 
     List below the number of Shares tendered or voted in favor of the Proposed
Amendment but not tendered by each beneficial owner whose tender or vote you
have solicited. All Shares in a Series of Preferred beneficially owned by a
beneficial owner, whether in one account or several, and in however many
capacities, must be aggregated for purposes of completing the table below. Any
questions as to what constitutes beneficial ownership should be directed to the
Depositary. If the space below is inadequate, list the Shares in a separate
signed schedule and affix the list to this Notice of Solicited Tenders and
Proxies.
 
     PLEASE DO NOT COMPLETE THE SECTIONS OF THE TABLE HEADED "TO BE COMPLETED
ONLY BY DEPOSITARY."
 
     ALL NOTICES OF SOLICITED TENDERS SHOULD BE RETURNED TO, AND ALL QUESTIONS
CONCERNING THE NOTICES OF SOLICITED TENDERS SHOULD BE DIRECTED TO, THE
DEPOSITARY. ALL NOTICES OF SOLICITED TENDERS MUST BE RECEIVED BY THE DEPOSITARY
WITHIN THREE BUSINESS DAYS AFTER THE EXPIRATION DATE.
 
          BENEFICIAL HOLDERS OF LESS THAN        SHARES (TENDERS ONLY)
 
<TABLE>
<CAPTION>
                                     ------------------------------------------------------------------
                                        TO BE COMPLETED BY SOLICITING           TO BE COMPLETED ONLY
                                                   DEALER                         BY DEPOSITARY
                                                  NUMBER OF                  NUMBER OF
                                     SERIES OF     SHARES      VOI TICKET     SHARES        $ FEE
        BENEFICIAL OWNERS            PREFERRED    TENDERED      NUMBER*      ACCEPTED     PER SHARE
- -------------------------------------------------------------------------------------------------------
<S>                                  <C>          <C>          <C>           <C>          <C>       <C>
 Beneficial Owner No. 1
- -------------------------------------------------------------------------------------------------------
 Beneficial Owner No. 2
- -------------------------------------------------------------------------------------------------------
 Beneficial Owner No. 3
- -------------------------------------------------------------------------------------------------------
 Beneficial Owner No. 4
- -------------------------------------------------------------------------------------------------------
 Beneficial Owner No. 5
- -------------------------------------------------------------------------------------------------------
 Total
- -------------------------------------------------------------------------------------------------------
</TABLE>
<PAGE>   5
 
           BENEFICIAL HOLDERS OF        OR MORE SHARES (TENDERS ONLY)
 
<TABLE>
<CAPTION>
                                     -----------------------------------------------------------------
                                        TO BE COMPLETED BY SOLICITING           TO BE COMPLETED ONLY
                                                   DEALER                           BY-DEPOSITARY
- ------------------------------------------------------------------------------------------------------
                                                  NUMBER OF                  NUMBER OF
                                     SERIES OF     SHARES      VOI TICKET     SHARES        $ FEE
        BENEFICIAL OWNERS            PREFERRED    TENDERED      NUMBER*      ACCEPTED     PER SHARE
- ------------------------------------------------------------------------------------------------------
<S>                                  <C>          <C>          <C>           <C>          <C>       <C>
 Beneficial Owner No. 1
- ------------------------------------------------------------------------------------------------------
 Beneficial Owner No. 2                                                                               
- ------------------------------------------------------------------------------------------------------
 Beneficial Owner No. 3                                                                               
- ------------------------------------------------------------------------------------------------------
 Beneficial Owner No. 4                                                                               
- ------------------------------------------------------------------------------------------------------
 Beneficial Owner No. 5                                                                               
- ------------------------------------------------------------------------------------------------------
 Total                                                                                                
- ------------------------------------------------------------------------------------------------------
</TABLE>
        
* Complete if Shares delivered by book-entry transfer. Please submit a 
  separate VOI ticket for Shares tendered when the solicitation fee is to be
  directed to another Soliciting Dealer. At the time of tendering Shares in
  book-entry form, please indicate your request in the comments field. 
                
            PROXY FOR BENEFICIAL HOLDERS OF LESS THAN        SHARES
                                                                   
<TABLE>
<CAPTION>
                                                  ----------------------------------------------------
                                                    TO BE COMPLETED BY         TO BE COMPLETED ONLY   
                                                    SOLICITING-DEALER              BY DEPOSITARY      
- ------------------------------------------------------------------------------------------------------
                                                               NUMBER OF    NUMBER OF                 
                                                  SERIES OF     SHARES       SHARES        $ FEE      
              BENEFICIAL OWNERS                   PREFERRED      VOTED      ACCEPTED     PER SHARE    
- ------------------------------------------------------------------------------------------------------
<S>                                               <C>          <C>          <C>          <C>       <C>
 Beneficial Owner No. 1                                                                               
- ------------------------------------------------------------------------------------------------------
 Beneficial Owner No. 2                                                                               
- ------------------------------------------------------------------------------------------------------
 Beneficial Owner No. 3                                                                               
- ------------------------------------------------------------------------------------------------------
 Beneficial Owner No. 4                                                                               
- ------------------------------------------------------------------------------------------------------
 Beneficial Owner No. 5                                                                               
- ------------------------------------------------------------------------------------------------------
 Total                                                                                                
- ------------------------------------------------------------------------------------------------------
</TABLE>
 
              PROXY FOR BENEFICIAL HOLDERS OF       OR MORE SHARES
 
<TABLE>
<CAPTION>
                                                  ----------------------------------------------------
                                                    TO BE COMPLETED BY         TO BE COMPLETED ONLY
                                                    SOLICITING-DEALER              BY DEPOSITARY
- ------------------------------------------------------------------------------------------------------
                                                               NUMBER OF    NUMBER OF
                                                  SERIES OF     SHARES       SHARES        $ FEE
              BENEFICIAL OWNERS                   PREFERRED      VOTED      ACCEPTED     PER SHARE
- ------------------------------------------------------------------------------------------------------
<S>                                               <C>          <C>          <C>          <C>       <C>
 Beneficial Owner No. 1
- ------------------------------------------------------------------------------------------------------
 Beneficial Owner No. 2
- ------------------------------------------------------------------------------------------------------
 Beneficial Owner No. 3
- ------------------------------------------------------------------------------------------------------
 Beneficial Owner No. 4
- ------------------------------------------------------------------------------------------------------
 Beneficial Owner No. 5
- ------------------------------------------------------------------------------------------------------
 Total
- ------------------------------------------------------------------------------------------------------
</TABLE>
 
     All questions as to the validity, form and eligibility (including time of
receipt) of any Notice of Solicited Tenders and Proxies will be determined by
the Depositary, in its sole discretion, which determination will be final and
binding. Neither the Depositary nor any other person will be under any duty to
give notification of


<PAGE>   6
 
any defects or irregularities in any Notice of Solicited Tenders or incur any
liability for failure to give such notification.
 
     PLEASE COMPLETE THE SIGNATURE FORM ON THE LAST PAGE.
 
     DO NOT SEND STOCK CERTIFICATES WITH THIS FORM. YOUR STOCK CERTIFICATES MUST
BE SENT WITH THE LETTER OF TRANSMITTAL AND PROXY.
 
     The undersigned hereby confirms that: (i) it has complied with the
applicable requirements of the Securities Exchange Act of 1934, as amended, and
the applicable rules and regulations thereunder, in connection with such
solicitation; (ii) it is entitled to such compensation for such solicitation
under the terms and conditions of the Offer; (iii) in soliciting tenders of
Shares, it has used no soliciting materials other than those furnished by IPC or
ILN; and (iv) if it is a foreign broker or dealer not eligible for membership in
the NASD, it has agreed to conform to the NASD's Rules of Fair Practice in
making solicitations.


 
- ------------------------                    ----------------------------       
Firm Name                                   Address (including Zip Code)   
                                
- ------------------------                    ------------------------------
By:                                         Area Code and Telephone Number 
Title:





<PAGE>   7
 
                 DO NOT SEND STOCK CERTIFICATES WITH THIS FORM.
                 YOUR STOCK CERTIFICATES MUST BE SENT WITH THE
                        LETTER OF TRANSMITTAL AND PROXY
- --------------------------------------------------------------------------------
 
                     SOLICITATION FEE PAYMENT INSTRUCTIONS
 
 Issue check to:
 
 Name:
      -------------------------------------------------------------------------
                                 (Please Print)
 
 Address:
         ----------------------------------------------------------------------

 
 ------------------------------------------------------------------------------
                               (Include Zip Code)

 
 ------------------------------------------------------------------------------
                (Taxpayer Identification or Social Security No.)

- --------------------------------------------------------------------------------

<PAGE>   1
 
                              ILLINOVA CORPORATION
                           OFFER TO PURCHASE FOR CASH
           ANY AND ALL OUTSTANDING SHARES OF THE FOLLOWING SERIES OF
                           CUMULATIVE PREFERRED STOCK
                                       OF
                             ILLINOIS POWER COMPANY
 
283,290 SHARES, CUMULATIVE PREFERRED STOCK,
 4.08% SERIES AT A PURCHASE PRICE OF $     PER SHARE, CUSIP NUMBER 452092 20 8
 
167,720 SHARES, CUMULATIVE PREFERRED STOCK,
 4.20% SERIES AT A PURCHASE PRICE OF $     PER SHARE, CUSIP NUMBER 452092 30 7
 
136,000 SHARES, CUMULATIVE PREFERRED STOCK,
 4.26% SERIES AT A PURCHASE PRICE OF $     PER SHARE, CUSIP NUMBER 452092 40 6
 
134,400 SHARES, CUMULATIVE PREFERRED STOCK,
 4.42% SERIES AT A PURCHASE PRICE OF $     PER SHARE, CUSIP NUMBER 452092 50 5
 
176,000 SHARES, CUMULATIVE PREFERRED STOCK,
 4.70% SERIES AT A PURCHASE PRICE OF $     PER SHARE, CUSIP NUMBER 452092 60 4
 
241,700 SHARES, CUMULATIVE PREFERRED STOCK,
 7.75% SERIES AT A PURCHASE PRICE OF $     PER SHARE, CUSIP NUMBER 452092 79 4
 
       THE OFFER AND WITHDRAWAL RIGHTS WILL EXPIRE AT 5:00 P.M., NEW YORK
       CITY TIME, ON                     , UNLESS THE OFFER IS EXTENDED.
 
                                                                [STATEMENT DATE]
 
To Our Clients:
 
     Enclosed for your consideration are the Offer to Purchase and Proxy
Statement, dated [STATEMENTDATE] (the "Offer to Purchase and Proxy Statement"),
a Proxy and a separate Letter of Transmittal and Proxy for each series of
cumulative preferred stock listed above (each a "Series of Preferred" and the
holder thereof a "Preferred Shareholder") of Illinois Power Company, an Illinois
corporation ("IPC") and direct utility subsidiary of Illinova Corporation, an
Illinois corporation ("ILN"), of which you own shares. As to each Series of
Preferred, the Offer to Purchase and Proxy Statement, together with the
applicable Letter of Transmittal and Proxy, constitutes the "Offer" of ILN to
purchase any and all shares of the Series of Preferred ("Shares") at the
purchase price per Share listed above, net to the seller in cash, upon the terms
and subject to the conditions of the Offer. ILN will purchase any and all Shares
validly tendered and not withdrawn, upon the terms and subject to the conditions
of the Offer. The Offer for a Series of Preferred is not conditioned upon any
minimum number of Shares of such Series of Preferred being tendered and is
independent of the Offer for any other Series of Preferred. While Preferred
Shareholders who wish to tender their Shares pursuant to the Offer need not vote
in favor of the proposed amendment to IPC's Amended and Restated Articles of
Incorporation, as set forth in the Offer to Purchase and Proxy Statement (the
"Proposed Amendment"), the Offer is conditioned upon the Proposed Amendment
being approved and adopted at the Special Meeting (as defined in the Offer to
Purchase and Proxy Statement). IPC's Board of Directors recommends voting in
favor of the Proposed Amendment. In addition, Preferred Shareholders have the
right to vote for the Proposed Amendment regardless of whether they tender their
Shares. If the Proposed Amendment is adopted by IPC's shareholders, IPC will
make a special cash payment in the amount of $
per Share to each Preferred Shareholder who voted in favor of the Proposed
Amendment, provided that such Shares have not been tendered pursuant to the
Offer. See "Proposed Amendment and Proxy Solicitation", "Terms of the Offer --
Certain Conditions of the Offer" and "Terms of the Offer -- Extension of Tender
Period; Termination; Amendments" in the Offer to Purchase and Proxy Statement.
<PAGE>   2
 
     WE ARE THE HOLDER OF RECORD OF SHARES HELD FOR YOUR ACCOUNT BUT NOT
REGISTERED IN YOUR NAME. A TENDER OR A VOTE OF SUCH SHARES CAN BE MADE ONLY BY
US AS THE HOLDER OF RECORD AND PURSUANT TO YOUR INSTRUCTIONS. ANY LETTER OF
TRANSMITTAL AND PROXY OR SEPARATE PROXY FURNISHED TO YOU IS SOLELY FOR YOUR
INFORMATION AND CANNOT BE USED BY YOU TO TENDER OR VOTE SHARES HELD BY US FOR
YOUR ACCOUNT.
 
     We request instructions as to whether you wish us to tender and/or vote any
or all of the Shares held by us for your account, upon the terms and subject to
the conditions set forth in the Offer.
 
     PLEASE READ THE FOLLOWING INFORMATION CAREFULLY:
 
     (1) The Offer is for any and all Shares outstanding as of [STATEMENT DATE].
The Offer for a Series of Preferred is independent of the Offer for any other
Series of Preferred.
 
     (2) The Offer and withdrawal rights will expire at 5:00 p.m., New York City
time, on [EXPIRATION DATE], unless the Offer is extended with respect to a
Series of Preferred. Your instructions to us should be forwarded to us in ample
time to permit us to submit a tender on your behalf by the expiration of the
Offer. If you would like to withdraw your Shares that we have tendered, you can
withdraw them so long as the Offer remains open or at any time after the
expiration of forty business days from the commencement of the Offer if such
tendered Shares have not been accepted for payment.
 
     (3) While Preferred Shareholders who wish to tender their Shares pursuant
to the Offer need not vote in favor of the Proposed Amendment, the Offer is
conditioned upon the Proposed Amendment being approved and adopted at the
Special Meeting.
 
     (4) Preferred Shareholders have the right to vote for the Proposed
Amendment regardless of whether they tender their Shares. If the Proposed
Amendment is adopted at the Special Meeting, IPC will make a special cash
payment in the amount of $  per Share to each Preferred Shareholder who voted in
favor of the Proposed Amendment, provided that such Shares have not been
tendered pursuant to the Offer.
 
     (5) Any stock transfer taxes applicable to the sale of Shares to ILN
pursuant to the Offer will be paid by ILN, except as otherwise provided in
Instruction 6 of the Letter of Transmittal and Proxy.
 
     NEITHER ILN, IPC, THEIR RESPECTIVE BOARDS OF DIRECTORS NOR ANY OF THEIR
RESPECTIVE OFFICERS MAKES ANY RECOMMENDATION TO ANY PREFERRED SHAREHOLDER AS TO
WHETHER TO TENDER ANY OR ALL SHARES. EACH PREFERRED SHAREHOLDER MUST MAKE HIS OR
HER OWN DECISION AS TO WHETHER TO TENDER SHARES AND, IF SO, HOW MANY SHARES TO
TENDER.
 
     If you wish to have us tender and/or vote any or all of your Shares held by
us for your account upon the terms and subject to the conditions set forth in
the Offer, please so instruct us by completing, executing, detaching and
returning to us the instruction form on the detachable part hereof. An envelope
to return your instructions to us is enclosed. If you authorize tender of your
Shares, all such Shares will be tendered unless otherwise specified on the
detachable part hereof. Your instructions should be forwarded to us in ample
time to permit us to submit a tender and/or vote on your behalf by the
expiration of the Offer or the Special Meeting, as applicable.
 
     The Offer is being made to all holders of Shares. ILN is not aware of any
state where the making of the Offer is prohibited by administrative or judicial
action pursuant to a valid state statute. If ILN becomes aware of any valid
state statute prohibiting the making of the Offer, ILN will make a good faith
effort to comply with such statute. If, after such good faith effort, ILN cannot
comply with such statute, the Offer will not be made to, nor will tenders be
accepted from or on behalf of, holders of Shares in such state. In those
jurisdictions where the securities, blue sky or other laws require the Offer to
be made by a licensed broker or dealer, the Offer shall be deemed to be made on
behalf of ILN by the Dealer Manager (as defined in the Offer) or one or more
registered brokers or dealers licensed under the laws of such jurisdictions.
<PAGE>   3
 
                                  INSTRUCTIONS
                   WITH RESPECT TO OFFER TO PURCHASE FOR CASH
                         ANY AND ALL OUTSTANDING SHARES
                                       OF
                              THE PREFERRED STOCK
                                      OF,
                             AND PROXY SOLICITATION
                                       BY
 
                             ILLINOIS POWER COMPANY
 
     The undersigned acknowledge(s) receipt of your letter and the enclosed
Offer to Purchase and Proxy Statement, dated [STATEMENT DATE], Proxy and a
separate Letter of Transmittal and Proxy for each series of preferred stock of
Illinois Power Company (each a "Series of Preferred") in which the undersigned
owns shares (as to each Series of Preferred, the Offer to Purchase and Proxy
Statement, together with the applicable Letter of Transmittal and Proxy,
constitutes the "Offer") in connection with the invitation of Illinova
Corporation ("ILN") to the holders of each Series of Preferred to tender any and
all of their shares of a Series of Preferred ("Shares") for purchase at the
purchase price per Share listed on the front cover of the Offer to Purchase and
Proxy Statement, net to the seller in cash, upon the terms and subject to the
conditions of the Offer, and in connection with the proxy solicitation being
conducted by the Board of Directors of Illinois Power Company.
 
     This will instruct you to tender to ILN the number of Shares indicated
below (or, if no number is indicated below, all Shares) which are held by you
for the account of the undersigned, upon the terms and subject to the conditions
of the Offer.
 
                              SERIES OF PREFERRED
 
- ------------------------------------------------------
 
- ------------------------------------------------------
 
- ------------------------------------------------------
 
- ------------------------------------------------------
 
- ------------------------------------------------------
                        NUMBER OF SHARES TO BE TENDERED*
 
- ------------------------------------------------------
 
- ------------------------------------------------------
 
- ------------------------------------------------------
 
- ------------------------------------------------------
 
- ------------------------------------------------------
 
     You are further instructed to vote as designated hereunder in respect of
the Proposed Amendment all shares which the undersigned is entitled to vote at
the Special Meeting:**
 
         [ ]  FOR               [ ]  AGAINST               [ ]  ABSTAIN
 
                                                         SIGN HERE
 
                                            ------------------------------------
                                                       Signature(s):
 
                                            ------------------------------------
                                                          Name(s):
 
                                            ------------------------------------
                                                          Address:
 
                                            ------------------------------------
                                                Social Security or Taxpayer
                                                    Identification No.:
 
                                            Dated:  , 1998
- -------------------------
 * By executing and returning these Instructions, unless otherwise indicated, it
   will be assumed that all Shares held by us for your account are to be
   tendered.
** By executing and returning these Instructions, unless otherwise indicated, it
   will be assumed that all Shares held by us for your account are to be voted
   FOR the Proposed Amendment.

<PAGE>   1
 
                                                                [STATEMENT DATE]
 
Dear Preferred Shareholder:
 
     Enclosed for your consideration is information regarding two proposals
relating to Illinois Power Company ("IPC") and your investment in shares of
preferred stock of IPC. First, the Board of Directors of IPC is soliciting
proxies for use at a special meeting of shareholders to be held on [EXPIRATION
DATE] at 4:30 p.m., New York City time, at the principal office of IPC located
at 500 South 27th Street, Decatur, Illinois 62525, to amend IPC's Articles of
Incorporation to remove a provision which limits the ability of IPC to issue or
assume unsecured indebtedness (the "Proposed Amendment"). Second, IPC's parent
holding company, Illinova Corporation ("ILN") is offering to purchase all of the
outstanding shares of preferred stock of IPC (the "Offer to Purchase"). If you
vote in favor of the Proposed Amendment and it is adopted at the Special
Meeting, you will be entitled to receive from IPC a special cash payment
("Special Cash Payment") of $       for each share you vote, provided your
shares have not been tendered in the Offer to Purchase. Both the Offer to
Purchase and the proxy solicitation for the Proposed Amendment are more fully
described in the enclosed Offer to Purchase and Proxy Statement.
 
     In connection with the Offer to Purchase and the proxy solicitation for the
Proposed Amendment, we ask that you consider the following:
 
     1. If you wish to accept the Offer to Purchase and tender your shares:
 
      - Complete, sign, and date the appropriate Letter of Transmittal and Proxy
        in accordance with the instructions in the Letter of Transmittal and
        Proxy.
 
      - Enclose your completed Letter of Transmittal and Proxy and related
        certificates for your shares in the brown envelope addressed to First
        Chicago Trust Company of New York at the appropriate address set forth
        on the back cover of the enclosed Offer to Purchase and Proxy Statement.
 
      - Please note that the Letter of Transmittal and Proxy should be used to
        vote on the Proposed Amendment if you are tendering Shares.
 
      PLEASE BE AWARE THAT THE OFFER TO PURCHASE IS CONDITIONED UPON ADOPTION OF
      THE PROPOSED AMENDMENT AT THE SPECIAL MEETING. A FAILURE TO RETURN A PROXY
      IS A VOTE AGAINST THE PROPOSED AMENDMENT. (Please also note that you
      cannot receive a Special Cash Payment if you tender your shares in the
      Offer to Purchase).
 
     2. If you wish to receive the Special Cash Payment:
 
      - Please vote, sign and date the [PROXY CARD COLOR] Proxy card. PLEASE BE
        AWARE THAT YOU MUST VOTE IN FAVOR OF THE PROPOSED AMENDMENT AND IT MUST
        BE ADOPTED IN ORDER FOR YOU TO RECEIVE A SPECIAL CASH PAYMENT. A FAILURE
        TO RETURN A PROXY IS A VOTE AGAINST THE PROPOSED AMENDMENT. (Please also
        note that you cannot receive a Special Cash Payment if your tender your
        shares in the Offer to Purchase.)
 
      - Enclose your completed Proxy card in the white envelope addressed to
        First Chicago Trust Company of New York at the appropriate address set
        forth on the back cover of the enclosed Offer to Purchase and Proxy
        Statement.
 
     If you have any questions on how to tender or vote your shares, please
contact:
 
                                          MacKenzie Partners, Inc. at:
                                          (800) 322-2885 (Toll Free)
                                          (212) 929-5500 (Call Collect)

<PAGE>   1
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                              CREDIT AGREEMENT

                            dated as of June 12, 1996

                                      among

                              ILLINOVA CORPORATION,

                         VARIOUS FINANCIAL INSTITUTIONS

                                       and

                                   CIBC INC.,
                            as Administrative Agent,

                                      with

               CIBC INC. and FIRST CHICAGO CAPITAL MARKETS, INC.,
                                as Co-Arrangers,

                                       and

                      FIRST CHICAGO CAPITAL MARKETS, INC.,
                              as Syndication Agent


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<PAGE>   2



                                CREDIT AGREEMENT


         This CREDIT AGREEMENT, dated as of June 12, 1996 (as amended or
otherwise modified from time to time, this "Agreement"), is entered into among
ILLINOVA CORPORATION, an Illinois corporation (the "Company"), the undersigned
financial institutions (collectively the "Lenders" and individually each a
"Lender") and CIBC INC. (in its individual capacity, "CIBC"), as administrative
agent for the Lenders, with CIBC and FIRST CHICAGO CAPITAL MARKETS, INC., as
Co-Arrangers, and FIRST CHICAGO CAPITAL MARKETS, INC., as Syndication Agent.

         In consideration of the premises and the mutual agreements herein
contained, and for other good and valuable consideration, the receipt and
sufficiency of which are hereby acknowledged, the parties hereto agree as
follows:

         SECTION 1 DEFINITIONS AND INTERPRETATION.

         1.1  Definitions. When used herein the following terms shall have the
following meanings (such definitions to be applicable to both the singular and
plural forms of such terms):

         Administrative Agent means CIBC in its capacity as administrative agent
for the Lenders hereunder and any successor thereto in such capacity.

         Affected Lender means any Lender that has given notice to the Company
(which has not been rescinded) of (i) any obligation by the Company to pay any
amount pursuant to Section 7.6 or 8.1 or (ii) the occurrence of any circumstance
of the nature described in Section 8.2 or 8.3.

         Affected Loan - see Section 8.3.

         Agents means, collectively, the Administrative Agent and the
Syndication Agent.

         Agreement - see the Preamble.

         Applicable Margin means, at any time, the percentage set forth in
Schedule II opposite the then-current Rating Level; it being understood that the
Applicable Margin shall adjust concurrently with any change in the applicable
Rating Level.

<PAGE>   3

         Assignee - see Section 14.6.1.

         Assignment Agreement - see Section 14.6.1.

         Business Day means any day (other than a Saturday or Sunday) on which
banks are open for commercial banking business in New York and, in the case of a
Business Day which relates to a Eurodollar Loan, on which dealings are carried
on in the New York eurodollar interbank market.

         Capital Lease means, with respect to any Person, any lease of (or other
agreement conveying the right to use) any real or personal property which, in
conformity with generally accepted accounting principles, is accounted for as a
capital lease on the balance sheet of such Person.

         CIBC - see the Preamble.

         Co-Arrangers means, collectively, CIBC and First Chicago
Capital Markets, Inc. as co-arrangers.

         Code means the Internal Revenue Code of 1986, as amended, and
regulations promulgated thereunder.

         Commitment as to any Lender means the commitment of such Lender to make
Loans hereunder, as adjusted from time to time pursuant to Section 6.1 or
Section 14.6. The amount of the initial Commitment of each Lender is set forth
on the Schedule I.

         Company - see the Preamble.

         Consolidated Net Worth means, at any date consolidated stockholders'
equity (excluding any equity attributed to any preferred stock) of the Company
and its Subsidiaries as at such date.

         Debt of any Person means, without duplication, (a) all indebtedness of
such Person for borrowed money, whether or not evidenced by bonds, debentures,
notes or similar instruments, (b) all obligations of such Person as lessee under
Capital Leases which have been recorded as liabilities on a balance sheet of
such Person, (c) all obligations of such Person to pay the deferred purchase
price of property or services (other than
 

                                      -2-

<PAGE>   4

current accounts payable in the ordinary course of business), (d) all
indebtedness secured by a Lien on the property of such Person, whether or not
such indebtedness shall have been assumed by such Person (it being understood
that if such Person has not assumed or otherwise become personally liable for
any such indebtedness, the amount of the Debt of such Person in connection
therewith shall be limited to the lesser of the face amount of such indebtedness
or the fair market value of all property of such Person securing such
indebtedness), (e) all obligations, contingent or otherwise, with respect to the
face amount of all letters of credit (whether or not drawn) and banker's
acceptances issued for the account of such Person, (f) all Suretyship
Liabilities of such Person and (g) all Debt (as defined above) of any
partnership in which such Person is a general partner.

         Dollar and the sign "$" mean lawful money of the United States of
America.

         Duff & Phelps Rating means, at any time, the rating issued by Duff &
Phelps Rating Co. and then in effect with respect to the First Mortgage Bonds.

         Effective Date - see Section 11.1.

         Environmental Laws means all federal, state or local laws, statutes,
common law duties, rules, regulations, ordinances and codes, together with all
administrative orders, directed duties, requests, licenses, authorizations and
permits of, and agreements with, any governmental authorities, in each case
relating to environmental, health, safety and land use matters.

         ERISA means the Employee Retirement Income Security Act of 1974, as
amended, and any successor statute of similar import, together with the
regulations thereunder, in each case as in effect from time to time. References
to sections of ERISA also refer to any successor sections.

         Eurocurrency Reserve Percentage means, for any day in any Interest
Period for any Eurodollar Loan of any Lender, the percentage in effect on such
day as prescribed by the Board of Governors of the Federal Reserve System (or
any successor thereto) or other U.S. government agency for determining the
reserve requirement (including, without limitation, any marginal, 

                                      -3-

<PAGE>   5

basic, supplemental or emergency reserves) for such Lender in respect of
liabilities or assets (with a term equal to such Interest Period) consisting of
or including "Eurocurrency liabilities" as currently defined in Regulation D or
any other applicable regulation or other liabilities or assets which such Lender
determines are actually maintained and attributable to or allocable to such
Eurodollar Loan. In determining such amount, each Lender may use any reasonable
averaging and attribution methods.

         Eurodollar Loan means any Loan which bears interest at a rate
determined by reference to the Eurodollar Rate.

         Eurodollar Office means with respect to any Lender the office or
offices of such Lender which shall be making or maintaining the Eurodollar Loans
of such Lender hereunder. A Eurodollar Office of any Lender may be, at the
option of such Lender, either a domestic or foreign office.

         Eurodollar Rate means, with respect to any Eurodollar Loan for any
Interest Period, the rate per annum at which Dollar deposits in immediately
available funds are offered to the New York office of CIBC two Business Days
prior to the beginning of such Interest Period by major banks in the interbank
eurodollar market as at or about 10:00 a.m., New York time, for delivery on the
first day of such Interest Period, for the number of days comprised therein and
in an amount equal or comparable to amount of the Eurodollar Loan of CIBC for 
such Interest Period.

         Existing Agreement means the Credit Agreement dated as of June 16, 1995
among the Company, various financial institutions, and CIBC, as agent.

         Event of Default means any of the events described in Section 12.1.

         Federal Funds Rate means, for any day, the rate set forth in the daily
statistical release designated as the Composite 3:30 p.m. Quotations for U.S.
Government Securities, or any successor publication, published by the Federal
Reserve Bank of New York (including any such successor publication, the
"Composite 3:30 p.m. Quotations") for such day under the caption "Federal Funds


                                      -4-

<PAGE>   6

Effective Rate". If such rate is not published in the Composite 3:30 p.m.
Quotations for any Business Day, the rate for such day will be the arithmetic
mean of the rates for the last transaction in overnight Federal funds arranged
prior to 9:00 a.m., New York City time, on such day by each of three leading
brokers of Federal funds transactions in New York City, selected by the
Administrative Agent. The rate for any day which is not a Business Day shall be
the rate for the immediately preceding Business Day.

         First Mortgage Bonds means the bonds issued pursuant to or secured by
(i) the Mortgage and Deed of Trust from Illinois Power to Harris Trust and
Savings Bank, as Trustee, dated as of November 1, 1943, and (ii) the General
Mortgage Indenture and Deed of Trust from the Company to Harris Trust and
Savings Bank, as Trustee, dated as of November 1, 1992.

         Floating Rate means at any time the greater of (a) the Federal Funds
Rate plus 1/2 of 1% and (b) the Prime Rate.

         Floating Rate Loan means any Loan which bears interest at or by
reference to the Floating Rate.

         Group - see Section 2.2.

         Illinois Power means Illinois Power Company, an Illinois
corporation.

         Interest Period - see Section 4.3.

         Lender - see the Preamble.

         Lien means, when used with respect to any Person, any interest of any
other Person in any real or personal property, asset or other right owned or
being purchased or acquired by such Person which secures payment or performance
of any obligation and shall include any mortgage, lien, encumbrance, charge or 
other security interest of any kind, whether arising by contract, as a matter 
of law, by judicial process or otherwise.

         Loan - see Section 2.1.

         Loan Documents means this Agreement and the Notes.


                                    -5-
<PAGE>   7

         Margin Stock means any "margin stock" as defined in 
Regulation G, T, U or X of the Board of Governors of the Federal Reserve System.

         Moody's Rating means, at any time, the rating issued by Moody's
Investors Service, Inc. and then in effect with respect to the First Mortgage
Bonds.


         Non-Use Fee Rate means the percentage set forth in Schedule II opposite
the then-current Rating Level; it being understood that the Non-Use Fee Rate
shall adjust concurrently with any change in the applicable Rating Level.

         Note - see Section 3.1.

         Participant - see Section 14.6.2.

         Percentage means as to any Lender the percentage which such Lender's
Commitment is of the aggregate Commitments (or, if the Commitments have
terminated, which the principal amount of such Lender's outstanding Loans is of
the principal amount of all outstanding Loans). The Percentages of the Lenders
as of the Effective Date are set forth on the Schedule I.

         Person means any natural person, corporation, partnership, trust,
association, governmental authority or unit, or any other entity, whether acting
in an individual, fiduciary or other capacity.

         Prime Rate means at any time the rate per annum then most recently
announced by CIBC as its prime rate at New York, New York.

         Rating Level means at any time the Level set forth in the table below
opposite the then-current Moody's Rating, S&P Rating or Duff & Phelps Rating,
whichever results in the numerically lower of the two highest (one being
highest) Levels; provided that if at any time there is no Moody's Rating or no
S&P Rating or no Duff & Phelps Rating, the Rating Level shall be Level 4.

                                       -6-

<PAGE>   8



                                                   Duff & Phelps
Level    Moody's Rating       S&P Rating              Rating
- -----    --------------       ----------              ------

 1       Baa1 or better       BBB+ or better          BBB+ or
                                                      better

 2       Baa2 or better but   BBB or better but    BBB or better 
         less than Baa1       less than BBB+       but less than 
                                                      BBB+
              
 3       Baa3 or better but   BBB- or better          BBB- or 
         less than Baa2       but less than BBB    better but 
                                                  less than BBB

 4       less than Baa3       less than BBB        less than 
                                                      BBB--

         Reportable Event means a "reportable event" as defined in Section 4043
of ERISA.

         Required Lenders means Lenders having an aggregate Percentage of
66-2/3% or more.

         SEC means the Securities and Exchange Commission.

         Significant Subsidiary means any Subsidiary of the Company which is a
"significant subsidiary" as defined in Regulation S-X of the SEC.

         S&P Rating means, at any time, the rating issued by Standard & Poor's
Ratings Services, a division of The McGraw-Hill Companies, Inc. and then in
effect with respect to the First
Mortgage Bonds.

         Stock Repurchase Capacity means the maximum amount of common stock of
Illinois Power which Illinois Power is permitted to repurchase pursuant to the
order of the Illinois Commerce Commission dated March 22, 1995, Docket No.
94-0518.

         Subsidiary means, with respect to any Person, any corporation of which
such Person and/or its other Subsidiaries own, directly or indirectly, such
number of outstanding shares as have not less than 50% of the ordinary voting
power for the election of directors. Unless the context otherwise requires, each
reference to Subsidiaries herein shall be a reference to Subsidiaries of the
Company.

                                      -7-

<PAGE>   9

         Suretyship Liability means any agreement, undertaking or other
contractual arrangement by which any Person guarantees, endorses or otherwise
becomes or is contingently liable upon (by direct or indirect agreement,
contingent or otherwise, to provide funds for payment, to supply funds to or
otherwise to invest in a debtor, or otherwise to assure a creditor against loss)
any indebtedness, obligation or other liability (including accounts payable) of
any other Person (other than by endorsements of instruments in the course of
collection), or guarantees the payment of dividends or other distributions upon
the shares of any other Person. The amount of any Person's obligation under any
Suretyship Liability shall (subject to any limitation set forth therein) be
deemed to be the principal amount of the indebtedness, obligation or other
liability guaranteed thereby; provided that the amount of any Person's
obligation under any Suretyship Liability relating to an interest rate swap,
currency swap, commodity swap or similar hedging arrangement shall be deemed to
be equal to the net liabilities of the primary obligor under all such
arrangements with the same counterparty calculated on a mark-to-market basis as
of the date of determination; and provided, further, that if the amount of any
Person's obligation under any Suretyship Liability is not determinable, the
amount thereof for purposes of this Agreement shall be the maximum reasonably
anticipated liability of such Person in respect thereof as reasonably estimated
by such Person as of the date of determination.

         Syndication Agent means First Chicago Capital Markets, Inc., in its
capacity as syndication agent.

         Termination Date means June 11, 1997 or such other date on which the
Commitments shall terminate pursuant to Section 6.1 or 12.2.

         Type of Loan or Borrowing - see Section 2.2. The types of Loans or
borrowings under this Agreement are as follows: Floating Rate Loans or
borrowings and Eurodollar Loans or borrowings.

         Unmatured Event of Default means any event which if it continues
uncured will, with lapse of time or notice or lapse of time and notice,
constitute an Event of Default.


                                      -8-

<PAGE>   10
     1.2 Computations. Where the character or amount of any asset or liability
or any item of income or expense is required to be determined, or any
consolidation or other accounting computation is required to be made, for
purposes of this Agreement, such determination or calculation shall, to the
extent applicable and except as otherwise specified in this Agreement, be made
in accordance with generally accepted accounting principles in effect from time
to time.

     1.3 Cross-References; Section Captions. A Section, an Exhibit or a Schedule
is, unless otherwise stated, a reference to a section hereof or an exhibit or
schedule hereto, as the case may be. Section captions are for convenience only
and shall not affect the interpretation of this Agreement.

     SECTION 2 COMMITMENTS OF THE LENDERS; TYPES OF LOANS;
               BORROWING AND CONVERSION PROCEDURES.

     2.1 Commitments. Subject to the terms and conditions of this Agreement,
each of the Lenders, severally and for itself alone, agrees to make loans to the
Company on a revolving basis (collectively the "Loans" and individually each a
"Loan") from time to time before the Termination Date in such Lender's
Percentage of such aggregate amounts as the Company may from time to time
request from all Lenders; provided, however, that (i) the aggregate principal
amount of all Loans which any Lender shall be committed to have outstanding
hereunder on loan to the Company shall not at any one time exceed the amount set
forth opposite such Lender's name on Schedule I hereto (as adjusted from time to
time pursuant to Section 6.1 and 14.6) and (ii) the aggregate principal amount
of all Loans which all Lenders shall be committed to have outstanding hereunder
on loan to the Company shall not at any one time exceed $100,000,000 (less any
reductions made pursuant to Section 6.1).

     2.2 Various Types of Loans. Each Loan shall be either a Floating Rate Loan
or a Eurodollar Loan (each a "type" of Loan), as the Company shall specify in
the related notice of borrowing or conversion pursuant to Section 2.3 or 2.4.
Eurodollar Loans having the same Interest Period are sometimes called a "Group"
or collectively "Groups". Floating Rate Loans and Eurodollar Loans may be
outstanding at the same time, provided that (i) not more than five different
Groups of Loans shall be outstanding at any

                                      -9-


<PAGE>   11

one time and (ii) the aggregate principal amount of each Group of Loans shall at
all times (including after giving effect to any conversion or continuation of
any Loans) be an integral multiple of $1,000,000.

     2.3 Borrowing Procedures. The Company shall give notice to the
Administrative Agent (which may be by telephone if promptly confirmed in
writing) of each proposed borrowing not later than (a) in the case of a Floating
Rate borrowing, 10:00 a.m., Chicago time, on the proposed date of such
borrowing, and (b) in the case of a Eurodollar borrowing, 10:00 a.m., Chicago
time, at least three Business Days prior to the proposed date of such borrowing.
Each such notice shall be effective upon receipt by the Administrative Agent and
shall specify the date, amount and type of borrowing and, in the case of a
Eurodollar borrowing, the initial Interest Period therefor. Promptly upon
receipt of such notice, the Administrative Agent shall advise each Lender
thereof. Not later than noon, New York time, on the date of a proposed
borrowing, each Lender shall provide the Administrative Agent at the principal
office of the Administrative Agent in New York with immediately available funds
covering such Lender's Percentage of such borrowing and, subject to the
satisfaction of the conditions precedent set forth in Section 11 with respect to
such borrowing, the Administrative Agent shall pay over such funds to the
Company on the requested borrowing date. Each borrowing shall be on a Business
Day.

     2.4 Conversion Procedures. Subject to the last sentence of Section 2.2, the
Company may convert all or any part of any outstanding Loan into a Loan of a
different type by giving notice (which may be by telephone if promptly confirmed
in writing) to the Administrative Agent not later than (a) in the case of
conversion into a Floating Rate Loan, 10:00 a.m., Chicago time, on the proposed
date of such conversion, and (b) in the case of a conversion into a Eurodollar
Loan, 10:00 a.m., Chicago time, at least three Business Days prior to the
proposed date of such conversion. Each such notice shall be effective upon
receipt by the Administrative Agent and shall specify the date and amount of
such conversion, the Loan to be so converted, the type of Loan to be converted
into and, in the case of a conversion into a Eurodollar Loan, the initial
Interest Period therefor. Promptly upon receipt of such notice, the
Administrative Agent shall advise each Lender thereof. Subject to Section 2.6,
such Loan

                                      -10-

<PAGE>   12

shall be so converted on the requested date of conversion. Each conversion shall
be on a Business Day.

     2.5 Warranty upon Conversion. Each notice of conversion pursuant to Section
2.4 shall automatically constitute a warranty by the Company to the
Administrative Agent and each Lender to the effect that, on the date of such
requested conversion, no Event of Default or Unmatured Event of Default shall
have then occurred and be continuing.

     2.6 Conditions. Notwithstanding any other provision of this Agreement, no
Lender shall be obligated to make any Loan, or to convert into or permit the
continuation at the end of the applicable Interest Period of any Eurodollar
Loan, if an Event of Default or Unmatured Event of Default exists or would
result therefrom.

     2.7 Pro Rata Treatment. All borrowings, conversions and repayments shall be
effected so that after giving effect thereto each Lender will have a pro rata
share (according to its Percentage) of all types and Groups of Loans.

     2.8 Commitments Several. The failure of any Lender to make a requested Loan
on any date shall not relieve any other Lender of its obligation (if any) to
make a Loan on such date, but no Lender shall be responsible for the failure of
any other Lender to make any Loan to be made by such other Lender.

     SECTION 3   NOTES EVIDENCING LOANS.

     3.1 Notes. The Loans of each Lender shall be evidenced by a promissory note
(as amended, supplemented, replaced or otherwise modified from time to time,
individually each a "Note" and collectively for all Lenders the "Notes")
substantially in the form set forth in Exhibit A, with appropriate insertions,
dated the Effective Date (or such other date as shall be satisfactory to the
Administrative Agent), payable to the order of such Lender in the principal
amount of the Commitment of such Lender (or, if less, in the aggregate unpaid
principal amount of such Lender's Loans) on the Termination Date.

     3.2 Recordkeeping. Each Lender shall record in its records, or at its
option on the schedule attached to its Note,

                                      -11-

<PAGE>   13


the date and amount of each Loan made by such Lender, each repayment or
conversion thereof and, in the case of each Eurodollar Loan, the dates on which
each Interest Period for such Loan shall begin and end. The aggregate unpaid
principal amount so recorded shall be rebuttable presumptive evidence of the
principal amount owing and unpaid on such Note. The failure to so record any
such amount or any error in so recording any such amount shall not, however,
limit or otherwise affect the obligations of the Company hereunder or under any
Note to repay the principal amount of the Loans evidenced by such Note together
with all interest accruing thereon.

     SECTION 4 INTEREST.

     4.1 Interest Rates. (a) The Company promises to pay interest on the unpaid
principal amount of each Loan for the period commencing on and including the
date of such Loan to but excluding the date such Loan is paid in full, as
follows:

                  (i) at all times while such Loan is a Floating Rate Loan, at a
         rate per annum equal to the Floating Rate from time to time in effect;
         and

                  (ii) at all times while such Loan is a Eurodollar Loan, at a
         rate per annum equal to the Eurodollar Rate applicable to each Interest
         Period for such Loan plus the Applicable Margin;

provided, however, that after maturity of any Loan (whether by acceleration or
otherwise), such Loan shall bear interest on the unpaid principal amount thereof
at a rate per annum equal to the Prime Rate from time to time in effect (but not
less than the interest rate in effect for such Loan immediately prior to
maturity) plus 2%.

         (b) The Company also promises to pay, to each Lender that incurs
reserve requirements as a consequence of funding any Eurodollar Loan, additional
interest on such Eurodollar Loan at a rate per annum equal to the excess of (i)
the rate obtained by dividing the Eurodollar Rate applicable to each Interest
Period for such Loan by a percentage (expressed as a decimal) equal to 100%
minus the Eurocurrency Reserve Percentage for such Lender for such Interest
Period over (ii) the Eurodollar Rate for such

                                      -12-

<PAGE>   14

Interest Period; it being understood that each Lender shall invoice the Company
(and provide a copy of such invoice to the Administrative Agent), from time to
time for the interest due to such Lender pursuant to this Section 4.1(b), which
invoice shall be (x) payable within 10 days after receipt thereof by the Company
and (y) accompanied by a statement setting forth in reasonable detail the
computation of such additional interest and shall be conclusive and binding upon
the parties hereto, in the absence of demonstrable error.

     4.2 Interest Payment Dates. Accrued interest on each Floating Rate Loan
shall be payable on the last day of each calendar quarter and at maturity.
Accrued interest on each Eurodollar Loan shall be payable on the last day of
each Interest Period relating to such Loan (and, in the case of any Eurodollar
Loan with an Interest Period exceeding three months, on each three-month
anniversary of the first day of such Interest Period) and at maturity. After
maturity, accrued interest on all Loans shall be payable on demand.

     4.3 Interest Periods. Each "Interest Period" for a Eurodollar Loan shall
commence on the date such Eurodollar Loan is made or converted from a Floating
Rate Loan, or on the expiration of the immediately preceding Interest Period for
such Eurodollar Loan, and shall end on the date which is one, two, three or six
months thereafter, as the Company may specify:


                  (a) in the case of an Interest Period which commences on the
         date a Eurodollar Loan is made or converted from a Floating Rate Loan,
         in the related notice of borrowing or conversion pursuant to Section
         2.3 or 2.4, or

                  (b) in the case of a succeeding Interest Period with respect
         to any Eurodollar Loan, by notice to the Administrative Agent (which
         may be by telephone if promptly confirmed in writing) not later than
         10:00 a.m., Chicago time, at least three Business Days prior to the
         first day of such succeeding Interest Period, it being understood that
         (i) each such notice shall be effective upon receipt by the
         Administrative Agent (which shall promptly advise each Lender thereof)
         and (ii) if the Company fails to give such notice, such Loan shall
         automatically become a Floating Rate Loan at the end of its
         then-current Interest Period.

                                      -13-

<PAGE>   15

Each Interest Period for a Eurodollar Loan that begins on the last day of a
calendar month (or on a day for which there is no numerically corresponding day
in the appropriate subsequent month) shall end on the last Business Day of the
appropriate subsequent calendar month. Each Interest Period for a Eurodollar
Loan which would otherwise end on a day which is not a Business Day shall end on
the immediately succeeding Business Day (unless such immediately succeeding
Business Day is in another calendar month, in which case such Interest Period
shall end on the immediately preceding Business Day). The Company may not select
any Interest Period which would end after the scheduled Termination Date.

     4.4 Setting and Notice of Eurodollar Rates. The applicable Eurodollar Rate
for each Interest Period shall be determined by the Administrative Agent, and
notice thereof shall be given by the Administrative Agent promptly to the
Company and each Lender. Each determination of the applicable Eurodollar Rate by
the Administrative Agent shall be conclusive and binding upon the parties
hereto, in the absence of demonstrable error. The Administrative Agent shall,
upon written request of the Company or any Lender, deliver to the Company or
such Lender a statement showing the computations used by the Administrative
Agent in determining any applicable Eurodollar Rate hereunder.

     4.5 Computation of Interest. Interest shall be computed for the actual
number of days elapsed on the basis of a year of 360 days. The applicable
interest rate for each Floating Rate Loan shall change simultaneously with each
change in the Floating Rate.


     SECTION 5 FEES.

     5.1     Non-Use Fee. The Company agrees to pay to the Administrative Agent
for the account of each Lender a non-use fee for the period from and including
June 12, 1996 to but excluding the Termination Date in an amount equal to the
Non-Use Fee Rate multiplied by the daily average of the unused amount of such
Lender's Commitment. Such non-use fee shall be payable in arrears on the last
day of each calendar quarter and on the Termination Date for any period then
ending for which such nonuse fee shall not have been theretofore paid. The
non-use fee shall be computed for the actual number of days elapsed on the 

                                      -14-

<PAGE>   16
basis of a year of 360 days.

           Administrative Agent's Fees. The Company agrees to pay to the
Administrative Agent for its own account such fees as are agreed to from time to
time by the Company and the Administrative Agent.

     SECTION 6 REDUCTION OR TERMINATION OF THE COMMITMENTS;
               PREPAYMENTS.
     
     6.1 Reduction or Termination of the Commitments. The Company may from time
to time on at least five Business Days' prior written notice received by the
Administrative Agent (which shall promptly advise each Lender thereof)
permanently reduce the amount of the Commitments to an amount not less than the
aggregate unpaid principal amount of the Loans. Any such reduction shall be in
an amount that is an integral multiple of $1,000,000 and shall be pro rata among
the Lenders according to their respective Percentages. The Company may at any
time on like notice terminate the Commitments upon payment in full of all Loans
and all other obligations of the Company hereunder.

     6.2 Prepayments. The Company may from time to time prepay the Loans in
whole or in part, provided that (a) the Company shall give the Administrative
Agent (which shall promptly advise each Lender) written notice thereof not later
than noon, New York time, on the date of such prepayment, in the case of
Floating Rate Loans, and not less than three Business Days' prior to the date of
such prepayment, in the case of Eurodollar Loans, in each case specifying the
Loans to be prepaid and the date (which shall be a Business Day) and amount of
prepayment, (b) each partial prepayment of Loans shall be in an integral
multiple of $1,000,000 and (c) any prepayment of Eurodollar Loans on a day other
than the last day of an Interest Period therefor shall be subject to Section
8.4. After giving effect to any prepayment of Eurodollar Loans, each Group of
Eurodollar Loans shall be an integral multiple of $1,000,000.

     SECTION 7 MAKING AND PRORATION OF PAYMENTS; SETOFF; TAXES.

     7.1 Making of Payments. All payments of principal of or interest on the
Notes, and of all fees, shall be made by the Company to the Administrative Agent
in immediately available

                                      -15-

<PAGE>   17

funds at its office in New York not later than 1:00 p.m., New York time, on the
date due; and funds received after that hour shall be deemed to have been
received by the Administrative Agent on the immediately following Business Day.
The Administrative Agent shall promptly remit to each Lender its share of all
such payments received in collected funds by the Administrative Agent for the
account of such Lender.

     All payments under Sections 8.1 and 8.4 shall be made by the Company
directly to the Lender entitled thereto.

     7.2 Application of Certain Payments. Each payment of principal shall be
applied to such Loans as the Company shall direct by notice to be received by
the Administrative Agent on or before the date of such payment or, in the
absence of such notice, as the Administrative Agent shall determine in its
discretion. Concurrently with each remittance to any Lender of its share of any
such payment, the Administrative Agent shall advise such Lender as to the
application of such payment.

     7.3      Due Date Extension. If any payment of principal or interest with
respect to any of the Notes, or of any fee, falls due on a day which is not a
Business Day, then such due date shall be extended to the immediately following
Business Day and, in the case of principal, additional interest shall accrue and
be payable for the period of any such extension.

     7.4 Setoff. To the extent not prohibited by applicable law (and without
waiving any other rights of the Administrative Agent or any Lender), the
Administrative Agent and each Lender shall, upon the occurrence of any Event of
Default described in Section 12.1.4 or any Unmatured Event of Default that may
result in such an Event of Default, have the right to appropriate and apply to
the payment of any amount payable by the Company hereunder any and all balances,
credits, deposits, accounts or moneys of the Company then or thereafter with
such Person, other than as trustee or custodian for the benefit of Persons other
than the Company.

     7.5 Proration of Payments. If any Lender shall obtain by payment or other
recovery (whether voluntary, involuntary, by application of offset or otherwise)
on account of principal of or interest on any Note in excess of its pro rata
share of payments


                                      -16-


<PAGE>   18


and other recoveries obtained by all Lenders on account of principal of and
interest on all Notes (other than any non-pro rata interest payment resulting
from a Loan being an Affected Loan or as a result of replacement of a Lender
pursuant to Section 8.7), such Lender shall purchase from the other Lenders such
participations in the Notes held by them as shall be necessary to cause such
purchasing Lender to share the excess payment or other recovery ratably with
each of them; provided, however, that if all or any portion of the excess
payment or other recovery is thereafter recovered from such purchasing Lender,
the purchase shall be rescinded and the purchase price restored to the extent of
such recovery.

              7.6 Payments Net of Taxes. All payments under this Agreement shall
be made without setoff or counterclaim and in such amounts as may be necessary
in order that all such payments (after deduction or withholding for or on
account of any present or future taxes, levies, imposts, duties, or other
charges of whatsoever nature imposed by any government or any political
subdivision or taxing authority thereof (collectively, "Taxes"), other than any
Taxes on or measured by the net income, net worth, or shareholder's capital of a
Lender pursuant to the income tax laws of the jurisdiction where such Lender's
principal office or Eurodollar Office is located) shall not be less than the
amounts otherwise specified to be paid under this Agreement and the Notes. A
certificate as to any additional amounts payable to any Lender under this
Section 7.6 submitted to the Company by such Lender shall show in reasonable
detail the amount payable and the calculations used to determine such amount,
and shall be conclusive and binding upon the parties hereto in the absence of
demonstrable error. With respect to each deduction or withholding for or on
account of any Taxes, the Company shall promptly (and in no event later than 45
days thereafter) furnish to each Lender such certificates, receipts and other
documents as may be required (in the reasonable judgment of such Lender) to
establish any tax credit to which such Lender may be entitled. All payments
under this Agreement shall be made under all circumstances, irrespective of
any bilateral or multilateral payment or clearing agreement that may be in
force, and of any restrictions then existing in any jurisdiction, and without
regard to the nationality, residence or domicile of any Lender, and without
requiring any affidavit or the fulfillment of any other formality. All
obligations provided for in this 

                                      -17-


<PAGE>   19


Section 7.6 shall survive repayment of the Loans, cancellation of the Notes or
any termination of this Agreement.

     SECTION 8  INCREASED COSTS; SPECIAL PROVISIONS FOR
                EURODOLLAR LOANS.

     8.1 Increased Costs. (a) If, after the date hereof, the adoption of any
applicable law, rule or regulation, or any change in any applicable law, rule or
regulation (including, without limitation, Regulation D of the Board of
Governors of the Federal Reserve System), or any change in the interpretation or
administration thereof by any governmental authority, central bank or comparable
agency charged with the interpretation or administration thereof, or compliance
by any Lender (or any Eurodollar Office of such Lender) with any request or
directive (whether or not having the force of law) of any such authority,
central bank or comparable agency

                  (A) shall subject any Lender (or any Eurodollar Office of such
         Lender) to any tax, duty or other charge with respect to its Eurodollar
         Loans, its Note or its obligation to make Eurodollar Loans, or shall
         change the basis of taxation of payments to any Lender of the principal
         of or interest on its Eurodollar Loans or any other amounts due under
         this Agreement in respect of its Eurodollar Loans or its obligation to
         make Eurodollar Loans (except for taxes imposed on or measured by the
         overall net income of such Lender or its Eurodollar Office imposed by
         the jurisdiction, or any political subdivision thereof or taxing
         authority therein, in which such Lender's principal executive office or
         Eurodollar Office is located or in which such Lender is incorporated);
         or

                  (B) shall impose, modify or deem applicable any reserve
         (including, without limitation, any reserve imposed by the Board of
         Governors of the Federal Reserve System, but excluding any reserve
         included in the determination of interest rates pursuant to Section 4),
         special deposit or similar requirement against assets of, deposits with
         or for the account of, or credit extended by any Lender (or any
         Eurodollar Office of such Lender); or

                  (C) shall impose on any Lender (or its Eurodollar

                                      -18-

<PAGE>   20



         Office) any other condition affecting its Eurodollar Loans,
         its Note or its obligation to make Eurodollar Loans;

and the result of any of the foregoing is to increase the cost to (or in the
case of Regulation D referred to above, to impose a cost on) such Lender (or any
Eurodollar Office of such Lender) of making or maintaining any Eurodollar Loan,
or to reduce the amount of any sum received or receivable by such Lender (or its
Eurodollar Office) under this Agreement or under its Note with respect thereto,
then within 10 days after demand by such Lender (which demand shall be
accompanied by a statement setting forth the basis of such demand, a copy of
which shall be furnished to the Administrative Agent), the Company shall pay
directly to such Lender such additional amount or amounts as will compensate
such Lender for such increased cost or such reduction.

         (b) If any Lender shall reasonably determine that the adoption or
phase-in of any applicable law, rule or regulation regarding capital adequacy,
or any change in any applicable law, rule or regulation, or any change in the
interpretation or administration thereof by any governmental authority, central
bank or comparable agency charged with the interpretation or administration
thereof, or compliance by any Lender (or its Eurodollar Office) or any Person
controlling such Lender with any request or directive regarding capital adequacy
(whether or not having the force of law) of any such authority, central bank or
comparable agency, has or would have the effect of reducing the rate of return
on such Lender's or such controlling Person's capital as a consequence of such
Lender's obligations hereunder (including, without limitation, such Lender's
Commitment) to a level below that which such Lender or such controlling Person
could have achieved but for such adoption, change or compliance (taking into
consideration such Lender's or such controlling Person's policies with respect
to capital adequacy) by an amount deemed by such Lender or such controlling
Person to be material, then from time to time, within 10 days after demand by
such Lender (which demand shall be accompanied by a statement setting forth the
basis of such demand, a copy of which shall be furnished to the Administrative
Agent), the Company shall pay to such Lender such additional amount or amounts
as will compensate such Lender or such controlling Person for such reduction.

     8.2 Basis for Determining Interest Rate Inadequate or

                                      -19-

<PAGE>   21


Unfair.  If with respect to any Interest Period:

         (a) deposits in Dollars (in the applicable amounts) are not being
offered to one or more Lenders in the London interbank eurodollar market for
such Interest Period, or the Administrative Agent otherwise reasonably
determines (which determination shall be binding and conclusive on the Company)
that by reason of circumstances affecting the London interbank eurodollar market
adequate and reasonable means do not exist for ascertaining the applicable 
Eurodollar Rate; or

         (b) Lenders having an aggregate Percentage of 30% or more advise the
Administrative Agent that the Eurodollar Rate as determined by the
Administrative Agent will not adequately and fairly reflect the cost to such
Lenders of maintaining or funding such Loans for such Interest Period, or that
the making or funding of Eurodollar Loans has become impracticable as a result
of an event occurring after the date of this Agreement which in the reasonable
opinion of such Lenders materially affects such Loans,

then the Administrative Agent shall promptly notify the other parties thereof
and, so long as such circumstances shall continue, (i) no Lender shall be under
any obligation to make or convert into Eurodollar Loans and (ii) on the last day
of the current Interest Period for each Eurodollar Loan, such Loan shall, unless
then repaid in full, automatically convert to a Floating Rate Loan.

           8.3 Changes in Law Rendering Eurodollar Loans Unlawful. In the 
event that any change in (including the adoption of any new) applicable laws or
regulations, or any change in the interpretation of applicable laws or
regulations by any governmental or other regulatory body charged with the
administration thereof, should make it (or in the good faith judgment of any
Lender cause a substantial question as to whether it is) unlawful for any
Lender to make, maintain or fund Eurodollar Loans, then such Lender shall
promptly notify each of the other parties hereto and, so long as such
circumstances shall continue, (a) such Lender shall have no obligation to make
or convert into Eurodollar Loans (but shall make Floating Rate Loans
concurrently with the making of or conversion into Eurodollar Loans by the
Lenders which are not so affected, in each case in 
        
                                      -20-

<PAGE>   22

an amount equal to such Lender's Percentage of all Eurodollar Loans which would
be made or converted into at such time in the absence of such circumstances) and
(b) on the last day of the current Interest Period for each Eurodollar Loan of
such Lender (or, in any event, if such Lender so requests, on such earlier date
as may be required by the relevant law, regulation or interpretation), such
Eurodollar Loan shall, unless then repaid in full, automatically convert to a
Floating Rate Loan. Each Floating Rate Loan made by a Lender which, but for the
circumstances described in the foregoing sentence, would be a Eurodollar Loan
(an "Affected Loan") shall, notwithstanding any other provision of this
Agreement, remain outstanding for the same period as the Group of Eurodollar
Loans of which such Affected Loan would be a part absent such circumstances.

     8.4  Funding Losses. The Company hereby agrees that upon demand by any
Lender (which demand shall be accompanied by a statement setting forth the basis
for the calculations of the amount being claimed, a copy of which shall be
furnished to the Administrative Agent) the Company will indemnify such Lender
against any net loss or expense which such Lender may sustain or incur
(including, without limitation, any net loss or expense incurred by reason of
the liquidation or reemployment of deposits or other funds acquired by such
Lender to fund or maintain any Eurodollar Loan), as reasonably determined by
such Lender, as a result of (a) any payment or prepayment or conversion of any
Eurodollar Loan of such Lender on a date other than the last day of an Interest
Period for such Loan (including, without limitation, any conversion pursuant to
Section 8.3) or (b) any failure of the Company to borrow or convert any Loans on
a date specified therefor in a notice of borrowing or conversion pursuant to
this Agreement (other than as a result of a default by such Lender or the
Administrative Agent). For this purpose, all notices to the Administrative Agent
pursuant to this Agreement shall be deemed to be irrevocable.

     8.5  Right of Lenders to Fund through Other Offices. Each Lender may, if
it so elects, fulfill its commitment as to any Eurodollar Loan by causing a
foreign branch or affiliate of such Lender to make such Loan, provided that in
such event for the purposes of this Agreement such Loan shall be deemed to have
been made by such Lender and the obligation of the Company to repay such Loan
shall nevertheless be to such Lender and shall be 

                                      -21-

<PAGE>   23


deemed held by it, to the extent of such Loan, for the account of such branch or
affiliate.


     8.6 Discretion of Lenders as to Manner of Funding. Notwithstanding any
provision of this Agreement to the contrary, each Lender shall be entitled to
fund and maintain its funding of all or any part of its Loans in any manner it
sees fit, it being understood, however, that for the purposes of this Agreement
all determinations hereunder shall be made as if such Lender had actually funded
and maintained each Eurodollar Loan during each Interest Period for such Loan
through the purchase of deposits having a maturity corresponding to such
Interest Period and bearing an interest rate equal to the Eurodollar Rate for
such Interest Period.

     8.7 Mitigation of Circumstances; Replacement of Affected Lender. (a) Each
Lender shall promptly notify the Company and the Administrative Agent of any
event of which it has knowledge which will result in, and will use reasonable
commercial efforts available to it (and not, in such Lender's sole judgment,
otherwise disadvantageous to such Lender) to mitigate or avoid, (i) any
obligation by the Company to pay any amount pursuant to Section 7.6 or 8.1 (ii)
the occurrence of any circumstance of the nature described in Section 8.2 or 8.3
(and, if any Lender has given notice of any such event described in clause (i)
or (ii) above and thereafter such event ceases to exist, such Lender shall
promptly so notify the Company and the Administrative Agent). Without limiting
the foregoing, each Lender will designate a different funding office if such
designation will avoid (or reduce the cost to the Company of) any event
described in clause (i) or (ii) of the preceding sentence and such designation
will not, in such Lender's sole judgment, be otherwise disadvantageous to such
Lender.

         (b) At any time any Lender is an Affected Lender, the Company may
replace such Affected Lender as a party to this Agreement with one or more other
bank(s) or financial institution(s) reasonably satisfactory to the
Administrative Agent, such bank(s) or financial institution(s) to have a
Commitment or Commitments, as the case may be, in such amounts as shall be
reasonably satisfactory to the Administrative Agent (and upon notice from the
Company such Affected Lender shall assign, without recourse or warranty, its
Commitment, its Loans, its Note

                                      -22-

<PAGE>   24

and all of its other rights and obligations hereunder to such replacement
bank(s) or other financial institution(s) for a purchase price equal to the sum
of the principal amount of the Loans so assigned, all accrued and unpaid
interest thereon, its ratable share of all accrued and unpaid non-use fees, any
amounts payable under Section 8.4 as a result of such Lender receiving payment
of any Eurodollar Loan prior to the end of an Interest Period therefor and all
other obligations owed to such Affected Lender hereunder).

     8.8 Conclusiveness of Statements; Survival of Provisions. Determinations
and statements of any Lender pursuant to Section 8.1, 8.2, 8.3 or 8.4 shall be
conclusive absent demonstrable error. Lenders may use reasonable averaging and
attribution methods in determining compensation under Sections 8.1 and 8.4, and
the provisions of such Sections shall survive repayment of the Loans,
cancellation of the Notes and any termination of this Agreement.

     SECTION 9  WARRANTIES.

     To induce the Administrative Agent and the Lenders to enter into this
Agreement and to induce the Lenders to make Loans hereunder, the Company
warrants to the Administrative Agent and the Lenders that:

     9.1 Organization, etc. The Company is a corporation duly incorporated,
validly existing and in good standing under the laws of the State of Illinois.

     9.2 Authorization; No Conflict. The execution and delivery of this
Agreement, the Notes and each other Loan Document to which it is a party, the
borrowings hereunder, and the performance by the Company of its obligations
under this Agreement, the Notes and each other Loan Document to which it is a
party are within the Company's corporate powers, will have been
duly authorized by all necessary corporate action prior to any borrowings
hereunder, have received all necessary governmental and regulatory approval, and
do not and will not contravene or conflict with, or result in the creation or
imposition of a Lien under, any provision of law or of the Articles of
Incorporation or by-laws of the Company or any Subsidiary or of any agreement,
instrument, order or decree that is binding upon the Company or 


                                      -23-

<PAGE>   25
any Subsidiary.

     9.3 Validity and Binding Nature. Each of this Agreement and each other Loan
Document to which the Company is a party is, or upon the execution and delivery
thereof will be, legal, valid, and binding obligations of the Company
enforceable against the Company in accordance with their respective terms,
except to the extent enforceability thereof is limited by bankruptcy, insolvency
or other laws relating to, or affecting the enforcement of, creditors' rights in
general, and by general principles of equity.

     9.4 Financial Statements. The Company's audited financial statements as at
December 31, 1995 and unaudited financial statements as at March 31, 1996,
copies of which have been furnished to each Lender, have been prepared in
conformity with generally accepted accounting principles applied on a basis
consistent with those of the preceding year, and present fairly the financial
position of the Company at such dates and the results of its operations for the
periods then ended.

     9.5 Conduct of Business. Since December 31, 1995, no event has occurred or
condition has arisen that has resulted in, or created a reasonable likelihood
of, a material adverse change in the business, properties, condition (financial
or otherwise), prospects or results of operations of the Company and its
Subsidiaries taken as a whole.

     9.6 Litigation and Contingent Liabilities. No litigation (including,
without limitation, derivative actions), arbitration proceedings or governmental
or regulatory proceedings are pending or threatened against the Company that
would, if adversely determined, materially and adversely affect the financial
condition, prospects, business, or operations of the Company and its
Subsidiaries taken as a whole, except as set forth in reports made by the
Company and filed with the SEC prior to the date of this Agreement, copies of
which have been furnished to each Lender. Other than any liability incident to
such litigation or proceedings, the Company does not have any material
contingent liabilities not provided for or disclosed in the financial statements
referred to in Section 9.4.

     9.7 Liens. None of the assets of the Company is subject to

                                      -24-

<PAGE>   26


any Lien, except as permitted pursuant to Section 10.14.


     9.8 Subsidiaries. Exhibit B correctly lists each Significant Subsidiary of
the Company owned as of the date hereof, and the state of incorporation of each
such Subsidiary. Each Subsidiary is duly incorporated, validly existing and in
good standing under the laws of the jurisdiction of its incorporation. All
Subsidiaries, except Illinois Power Fuel Company, are currently wholly-owned by
the Company or by Illinois Power, and all of the shares of stock of each
Subsidiary (including the shares of stock of Illinois Power Fuel Company that
are owned by Illinois Power) have been duly issued, are fully paid and
non-assessable, and are owned by the Company or by Illinois Power as of the date
hereof free and clear of any Lien.

     9.9 Employee Benefit Plans. Each employee benefit plan as to which the
Company may have any liability complies in all material respects with all
applicable requirements of law and regulations, and (i) to the best of the
Company's knowledge, no Reportable Event has occurred with respect to any such
plan, (ii) neither the Company nor any Subsidiary has withdrawn from any such
plan and (iii) no such plan has been terminated. Neither the execution and
delivery of this Agreement or any other Loan Document to which the Company is a
party nor the making of Loans hereunder will give rise to a prohibited
transaction within the meaning of Section 406 of ERISA or Section 4975 of the
Code.

     9.10 Investment Company Act. The Company is not an "investment company" or,
to the best of the Company's knowledge, a company "controlled" by an "investment
company", within the meaning of the Investment Company Act of 1940, as amended.

     9.11 Public Utility Holding Company Act. The Company and its Subsidiaries
are exempt from the provisions of the Public Utility Holding Company Act of
1935, as amended, except Section 9(a)(2) thereof, and, to the best of the
Company's knowledge, no proceedings to revoke or modify such exemption have been
instituted or are pending.

     9.12 Regulation U. The Company is not engaged principally, or as one of its
important activities, in the business of extending credit for the purpose of
purchasing or carrying Margin Stock.


                                      -25-

<PAGE>   27

     9.13 Debt. Exhibit C correctly sets forth all Debt of the Company as of the
date of this Agreement (or such other date as set forth on Exhibit C)(other than
items of Debt which individually do not exceed $1,000,000 and collectively do
not exceed $5,000,000).

     9.14 Taxes. The Company has filed all income or franchise tax returns and
reports required by law to have been filed by it and has paid all taxes and
governmental charges thereby shown to be owing, except for any such taxes or
charges which are being diligently contested in good faith by appropriate
proceedings and for which adequate reserves in accordance with generally
accepted accounting principles shall have been set aside on its books.

     9.15 Compliance with Laws. Except as set forth on Exhibit F, the Company is
not in violation of any law, ordinance, rule, regulation or order of any
governmental authority applicable to it or its property (including, without
limitation, any Environmental Law), except where any such violation would not
materially and adversely affect the financial condition, prospects, business, or
operations of the Company and its Subsidiaries taken as a whole.

     SECTION 10 COVENANTS.

     Until the expiration or termination of the Commitments, and thereafter
until all obligations of the Company hereunder and under the Loan Documents are
paid in full, the Company agrees that, unless at any time the Required Lenders
shall otherwise expressly consent in writing, it will:

     10.1 Reports, Certificates and Other Information. Furnish to each Lender:

             10.1.1  Annual Report. Within 90 days after each fiscal year of the
         Company, a copy of the annual report of the Company to the SEC on Form
         10-K. Concurrently with the delivery of each such annual report, the
         Company will furnish to each Lender the written statement of the
         certified public accountants whose opinion is contained in such annual
         report to the effect that in making the examination necessary for their
         opinion relating to the Company's financial statements contained in
         such annual 

                                      -26-


<PAGE>   28

         report (no other review having been conducted), they have obtained no
         knowledge of any event described in Section 12.1.1, 12.1.2 or 12.1.6,
         or of any other circumstance that such accountants should disclose in
         the exercise of then generally accepted auditing standards; or, if
         such accountants shall have obtained knowledge of any such event or
         any such other circumstance, they shall disclose in such statement the
         event(s) or circumstances(s) and the nature and status thereof.
        
             10.1.2 Interim Reports. Within 60 days after each quarter (except
         the last quarter) of each fiscal year of the Company, a copy of the
         quarterly report of the Company to the SEC on Form 10-Q, signed by a
         proper accounting officer of the Company.

             10.1.3  Certificates.  Contemporaneously with the furnishing of a 
         copy of each report provided for in Section 10.1.1 or 10.1.2, a 
         certificate dated the date of such report and signed by an authorized 
         officer of the Company, (a) to the effect that, to the best of his 
         knowledge, after diligent inquiry, no Event of Default or Unmatured 
         Event of Default has occurred and is continuing, or, if there is any 
         such event, describing it and the steps, if any, being taken to cure 
         it, and (b) containing a computation in reasonable detail of the 
         covenants set forth in Sections 10.11, 10.15 and 10.16 as of the end 
         of the applicable fiscal quarter or fiscal year.

             10.1.4 Reports to SEC and to Shareholders. Promptly upon their
         becoming available, copies of (i) each financial statement, report,
         notice or proxy statement sent by the Company to its stockholders
         generally, and (ii) each regular or periodic report or other report
         with respect to the institution of, or any adverse determination in,
         any litigation, arbitration proceeding, or governmental or regulatory
         proceeding, and any registration statement or prospectus (other than on
         or in respect of Form S-8 or any similar form) or similar document, in
         each case, filed by the Company with any securities exchange or with
         the SEC or any successor agency.

             10.1.5 Notice of Default and ERISA Matters. Forthwith 

                                      -27-


<PAGE>   29

          upon learning of the occurrence of any of the following, written
          notice thereof, describing the same and the steps being taken by the
          Company with respect thereto: (i) the occurrence of an Event of
          Default or an Unmatured Event of Default, or (ii) the occurrence of a
          Reportable Event Under, or the institution of steps by the Company or
          any Subsidiary to withdraw from or the institution of any steps to
          terminate, any employee benefit plan as to which the Company may have
          any liability.

             10.1.6 Significant Subsidiaries.  A written report of
         any changes in the list of its Significant Subsidiaries,
         promptly upon the occurrence thereof.

             10.1.7 Other Information.  From time to time, such
         other information concerning the Company and its
         Subsidiaries as any Lender or the Administrative Agent may
         reasonably request.

     10.2 Books, Records, and Inspections. Maintain complete and accurate books
and records; permit access by any Lender or the Administrative Agent to the
books and records of the Company; and permit any Lender or the Administrative
Agent to inspect the properties and operations of the Company.

     10.3 Insurance. Maintain such insurance as may be required by law, and
maintain such other insurance, to such extent and against such hazards and
liabilities, as is customarily maintained by companies similarly situated and
operating like properties.

     10.4 Taxes and Liabilities. Pay when due all taxes, assessments, and other
liabilities except as contested in good faith and by appropriate proceedings.

     10.5  Mergers, Consolidations, Sales. Not be a party to any merger or
consolidation, or purchase or otherwise acquire all or substantially all of the
assets or stock of any class of, or any partnership or joint venture interest
in, any other Person that if such Person had been a Subsidiary of the Company,
would be a Significant Subsidiary, or, except in the ordinary course of its
business, sell, transfer, convey or lease all or any substantial part of its
assets, except for any such merger or consolidation, 

                                      -28-

<PAGE>   30


sale, transfer, conveyance, lease or assignment of or by any wholly-owned
Subsidiary into the Company and any such purchase or other acquisition by the
Company of the assets or stock of any wholly-owned Subsidiary.

     10.6 Maintenance of Properties. Cause all properties used or useful in the
conduct of the business of the Company to be maintained, and kept in reasonable
condition, repair and working order, and cause to be made all necessary repairs,
renewals, replacements, betterments and improvements thereof, all as in the
judgment of the Company may be necessary so that the business carried on in
connection therewith may be properly and advantageously conducted at all times;
provided, however, that the Company shall not be prevented from discontinuing
the operation and maintenance of any such properties if such discontinuance is,
in the judgment of the Company, desirable in the operation of its business and
not disadvantageous in any material respect to any Lender.

     10.7 Conduct of Business. Carry out and conduct its business in
substantially the same manner and in substantially the same fields as
contemplated in the Company's Form 10-K filed with the SEC for the fiscal year
ended December 31, 1995, and do or cause to be done all things necessary to
preserve and keep in full force and effect the corporate existence, and the
rights (statutory and arising under its Articles of Incorporation) and
franchises, of the Company; provided, however, that the Company shall not be
required to preserve any such right or franchise if it determines that the
preservation thereof is no longer necessary or desirable in the conduct of its
business and that the loss thereof is not disadvantageous in any material
respect to the holder of any Note.

     10.8 Employee Benefit Plans. Maintain each employee benefit plan as to
which it may have any liability in compliance with all applicable requirements
of law and regulations.
 
     10.9 Use of Proceeds. Use the proceeds of all Loans only for the payment of
dividends, making investments in or acquisitions of non-regulated,
energy-related businesses, and for general corporate purposes; and not use any
proceeds of any Loan, or permit any such proceeds to be used, either directly or
indirectly, for the purpose, whether immediate, incidental or 

                                      -29-

<PAGE>   31

ultimate, of "purchasing or carrying" any Margin Stock.

     10.10 Other Agreements. Not enter into any agreement containing any
provision that would be violated or breached by the performance of its
obligations hereunder or under any instrument or document delivered or to be
delivered by it hereunder or in connection herewith.

     10.11 Restrictions on Debt. Not at any time permit all Debt of the Company
to exceed the product of 3 multiplied by the lesser of (a) the amount of
dividends paid to the Company during the period of four consecutive fiscal
quarters then most recently ended and (b) the aggregate net income of all
Subsidiaries of the Company during such period.

     10.12 Illinois Power. Cause Illinois Power to comply with all of the
covenants set forth in Section 9 of the Credit Agreement dated as of May 26,
1995 among Illinois Power, various financial institutions and Bank of America
National Trust and Savings Association, as agent, as such Credit Agreement is in
effect on the date hereof (without giving effect to (i) any termination thereof
or (ii) any amendment or other modification thereto unless consented to by the
Required Lenders). A copy of such Section 9 as in effect on the date hereof is
attached hereto as Exhibit H.

     10.13 Compliance with Laws. Comply in all material respects with all laws,
ordinances, rules, regulations or orders of any governmental authority having
jurisdiction over it or its business (including, without limitation, the Federal
Fair Labor Standards Act and Environmental Laws), except as such may be
contested in good faith by appropriate proceedings.

     10.14 Limitation on Liens. Not, and not permit any Significant Subsidiary
to create, incur, assume or permit to exist any Lien on any of its properties
(other than Liens on the common stock of Illinois Power so long as the
obligations of the Company hereunder are equally and ratably secured), except

         (a)  any Liens in existence as of the Effective Date and
listed on Exhibit G hereto;

         (b) Liens for taxes, assessments or other governmental 


                                      -30-

<PAGE>   32

charges or levies not yet due or which are being contested in good faith by
appropriate proceedings;

         (c) Liens in connection with workmen's compensation, unemployment
insurance or other social security, old age pension or similar obligations;

         (d) Liens in connection with any litigation or other legal proceeding
or arising out of a judgment or award, for sums not exceeding $5,000,000, with
respect to which an appeal is being prosecuted and the execution or other
enforcement of such Liens is effectively stayed;

         (e) landlord's, vendor's, carrier's, warehousemen's, repairmen's,
mechanic's, workmen's, materialmen's, construction or similar Liens;

         (f) easements, rights-of-way, restrictions and other similar
encumbrances which, in the aggregate, do not materially adversely interfere with
the occupation, use and enjoyment of the property encumbered thereby;

         (g) in the case of Illinois Power, (i) Liens arising pursuant to that
certain Mortgage and Deed of Trust from Illinois Power to Harris Trust and
Savings Bank, as Trustee, dated as of November 1, 1943, and "permitted liens" as
defined in such Mortgage, and (ii) Liens arising pursuant to that certain
General Mortgage Indenture and Deed of Trust from Illinois Power to Harris Trust
and Savings Bank, as Trustee, dated as of November 1, 1992, and "Permitted
Liens" as defined in such General Mortgage;

         (h) in the case of any Significant Subsidiary, Capital
Leases;

         (i) in the case of the Company, purchase money security interests and
Capital Leases, provided that the aggregate amount of the Debt secured thereby
shall not exceed $1,000,000; and

         (j) extensions, renewals or replacements of any Lien permitted by the
foregoing provisions of this Section 10.14, but only if the principal amount of
the Debt secured thereby immediately prior to such extension, renewal or
replacement is 


                                      -31-


<PAGE>   33

not increased and such Lien is not extended to any other property.

     10.15 Illinova Net Worth. Not permit Consolidated Net Worth to at any time
be less than $1,100,000,000.

     10.16 Illinois Power Stock Repurchase Capacity. Not permit Stock Repurchase
Capacity to at any time be less than $75,000,000.

 
     SECTION 11  CONDITIONS OF LENDING.

     The obligation of each Lender to make its Loans is subject to the
following conditions precedent:

     11.1 Initial Loan. The obligation of each Lender to make its initial Loan
is, in addition to the conditions precedent specified in Section 11.2, subject
to the conditions precedent (and the date on which all such conditions precedent
have been satisfied or waived in writing by the Lenders is herein called the
"Effective Date") that (i) the Existing Agreement shall have been terminated and
all amounts due and owing thereunder shall have been paid in full and (ii) the
Administrative Agent shall have received all of the following, each duly
executed and dated the Effective Date (or such other date as shall be
satisfactory to the Administrative Agent), in form and substance satisfactory to
the Administrative Agent, and each (except for the Notes, of which only the
originals shall be signed) in sufficient number of signed counterparts to
provide one for each Lender:

     11.1.1 Notes. The Notes of the Company payable to the order of the Lenders.

     11.1.2 Resolutions. Certified copies of resolutions of the Board of
Directors of the Company authorizing the execution, delivery and performance by
the Company of this Agreement, the Notes, the other Loan Documents and the other
documents to be executed by the Company pursuant hereto.

     11.1.3 Consents, etc. Certified copies of all documents evidencing any
consents and governmental approvals (if any) required for the execution,
delivery and performance by the Company of this Agreement, the Notes, the Loan
Documents and the 

                                      -32-

<PAGE>   34

other documents to be executed by the Company pursuant hereto.

   11.1.4  Incumbency and Signature Certificates. An incumbency and signature
certificate of the Company certifying the names of the officer or officers of
the Company authorized to sign this Agreement, the Notes, the Loan Documents and
the other documents required to be delivered by the Company in connection with
this Agreement, together with a sample of the true signature of each such
officer (it being understood that the Administrative Agent and each Lender may
conclusively rely on such certificate until formally advised by a like
certificate of any changes therein).

   11.1.5  Opinion of Counsel for the Company. The opinion of Schiff Hardin &
Waite, counsel to the Company, substantially in the form of Exhibit D.

   11.1.6  Other.  Such other documents as the Administrative
Agent or any Lender may reasonably request.

   11.2    All Loans.  The obligation of each Lender to make each
Loan is subject to the following further conditions precedent
that:

   11.2.1  No Default. (a) No Event of Default or Unmatured Event of Default has
occurred and is continuing or will result from the making of such Loan and (b)
the warranties of the Company contained in Section 9 (excluding (i) the second
sentence of Section 9.6, (ii) Section 9.8 and (iii) Section 9.9) are true and
correct in all material respects as of the date of the making of such requested
Loan, with the same effect as though made on such date.

   11.2.2  Satisfaction of Conditions Precedent. Each request by the Company for
the making of a Loan shall be deemed to constitute a warranty by the Company
that the conditions precedent set forth in Section 11.2.1 will be satisfied at
the time of the making of such Loan.

   SECTION 12  EVENTS OF DEFAULT AND THEIR EFFECT.

   12.1    Events of Default.  Each of the following shall constitute an Event 
of Default under this Agreement:

                                      -33-

<PAGE>   35

             12.1.1 Non-Payment of the Loans, etc. Default in the payment when
         due of the principal of any Loan; or default, and continuance thereof
         for five days, in the payment when due of any interest, fees or other
         amount payable by the Company hereunder or under any other Loan
         Document.

             12.1.2 Non-Payment of Other Debt. Any default shall occur under the
         terms applicable to any Debt of the Company or Illinois Power in an
         aggregate amount (for all Debt so affected) exceeding $10,000,000 or
         under the terms applicable to any Debt of any other Subsidiary in an
         aggregate amount (for all Debt so affected) exceeding $5,000,000 and
         such default shall (a) consist of the failure to pay such Debt when due
         (subject to any applicable grace period), whether by acceleration or
         otherwise, or (b) accelerate the maturity of such Debt or permit the
         holder or holders thereof, or any trustee or agent for such holder or
         holders, to cause such Debt to become due and payable prior to its
         expressed maturity.

             12.1.3 Warranties. Any warranty made by the Company herein is
         breached or is false or misleading in any material respect, or any
         schedule, certificate, financial statement, report, notice or other
         writing furnished by the Company to the Administrative Agent or any
         Lender is false or misleading in any material respect on the date as of
         which the facts therein set forth are stated or certified.

             12.1.4 Bankruptcy, Insolvency, etc. The Company or any Subsidiary
         becomes insolvent or generally fails to pay, or admits in writing its
         inability or refusal to pay, debts as they become due; or the Company
         or any Subsidiary applies for, consents to, or acquiesces in the
         appointment of a trustee, receiver or other custodian for the Company
         or such Subsidiary or any property thereof, or makes a general
         assignment for the benefit of creditors; or, in the absence of such
         application, consent or acquiescence, a trustee, receiver or other
         custodian is appointed for the Company or any Subsidiary or for a
         substantial part of the property of any thereof and is not discharged
         within 60 days; or any bankruptcy, reorganization, debt arrangement, or
         other case or proceeding under any bankruptcy or insolvency law, or any
         dissolution or liquidation proceeding (except the voluntary

                                      -34-

<PAGE>   36

         dissolution, not under any bankruptcy or insolvency law, of a
         Subsidiary other than Illinois Power), is commenced in respect of the
         Company or any Subsidiary, and if such case or proceeding is not
         commenced by the Company or such Subsidiary, it is consented to or
         acquiesced in by the Company or such Subsidiary, or remains for 60 days
         undismissed; or the Company or any Subsidiary takes any corporate or
         partnership action to authorize, or in furtherance of, any of the
         foregoing.

             12.1.5 Non-Compliance with Provisions of this Agreement. Failure by
         the Company to comply with or to perform any covenant set forth in
         Sections 10.1.5, 10.5, 10.9, 10.11, 10.12, 10.14, 10.15 and 10.16; or
         failure by the Company to comply with or to perform any other provision
         of this Agreement (and not constituting an Event of Default 
         under any of the other provisions of this Section 12) and continuance 
         of such failure for 30 days after notice thereof to the Company from 
         the Administrative Agent or any Lender.

             12.1.6 Employee Benefit Plans. With respect to any employee benefit
         plan as to which the Company or any Subsidiary may have any liability,
         there shall exist a deficiency of more than $20,000,000 in the plan
         assets available to satisfy the benefits guaranteeable under ERISA with
         respect to such plan, or such plan is terminated or the Company or any
         Subsidiary withdraws from such plan.

             12.1.7 Ownership of Significant Subsidiaries. The Company shall
         fail at any time to own, directly or indirectly, all of the capital
         stock of each Subsidiary which is at any time a Significant Subsidiary,
         in each case free and clear of any Lien.

             12.1.8 Judgments.  Final judgments which exceed an aggregate of 
         $10,000,000 shall be rendered against the Company, or any Subsidiary 
         and shall not have been discharged or vacated or had execution thereof 
         stayed pending appeal within 30 days after entry or filing of such 
         judgments.

             12.1.9 Change in Control. (a) Any Person or group of Persons
         (within the meaning of Section 13 or 14 of the

                                      -35-

<PAGE>   37

         Securities Exchange Act of 1934, as amended) shall acquire beneficial
         ownership (within the meaning of Rule 13d-3 promulgated under such
         Act) of 20% or more of the outstanding shares of common stock of the
         Company; or (b) during any 24-month period, individuals who at the
         beginning of such period constituted the Company's Board of Directors
         (together with any new directors whose election by the Company's Board
         of Directors or whose nomination for election by the Company's
         shareholders was approved by a vote of a majority of the directors who
         either were directors at the beginning of such period or whose
         election or nomination was previously so approved) cease for any
         reason to constitute a majority of the Board of Directors of the
         Company.

           12.1.10   Environmental. The Company or any of its Subsidiaries shall
         be the subject of any proceeding or investigation pertaining to the
         release by the Company or any of its Subsidiaries, or any other Person
         of any toxic or hazardous waste or substance into the environment, or
         there shall occur any violation of any Environmental Law, which, in
         either case, could materially and adversely affect the financial
         condition, prospects, business or operations of the Company and its
         Subsidiaries taken as a whole.

     12.2  Effect of Event of Default. If any Event of Default described in
Section 12.1.4 shall occur, the Commitments (if they have not theretofore
terminated) shall immediately terminate and the Notes and all other obligations
hereunder shall become immediately due and payable, all without presentment,
demand, protest or notice of any kind; and in the case of any other Event of
Default, the Administrative Agent may, and upon written request of the Required
Lenders shall, declare the Commitments (if they have not theretofore terminated)
to be terminated and/or declare all Notes and all other obligations hereunder to
be due and payable, whereupon the Commitments (if they have not theretofore
terminated) shall immediately terminate and/or all Notes and all other
obligations hereunder shall become immediately due and payable, all without
presentment, demand, protest or notice of any kind. The Administrative Agent
shall promptly advise the Company of any such declaration, but failure to do so
shall not impair the effect of such declaration. Notwithstanding the foregoing,
the effect as an Event of Default 

                                      -36-

<PAGE>   38

of any event described in Section 12.1.1 or Section 12.1.4 may be waived by the
written concurrence of all of the Lenders, and the effect as an Event of
Default of any other event described in this Section 12 may be waived by the
written concurrence of the Required Lenders.
        
     SECTION 13  THE ADMINISTRATIVE AGENT.

     13.1 Authorization. Each Lender authorizes the Administrative Agent to act
on behalf of such Lender to the extent provided herein or any other document or
instrument delivered hereunder or in connection herewith, and to take such other
action as may be reasonably incidental thereto.

     13.2 Indemnification. Each Lender agrees to reimburse and indemnify the
Administrative Agent for, and hold the Administrative Agent harmless against, a
share (determined in accordance with such Lender's Percentage) of any loss,
damage, penalty, action, judgment, obligation, cost, disbursement, liability or
expense (including reasonable attorneys' fees) which may at any time be incurred
by the Administrative Agent (and for which the Administrative Agent is not
reimbursed by the Company) arising out of or in connection with the performance
of its obligations or the exercise of its powers hereunder or any other document
or instrument delivered hereunder or in connection herewith, as well as the
costs and expenses of defending against any claim against the Administrative
Agent arising hereunder or thereunder, provided that no Lender shall be liable
for any of the foregoing which are determined by a court of competent
jurisdiction in a final proceeding to have resulted solely from the
Administrative Agent's gross negligence or willful misconduct.

     13.3 Exculpation. The Administrative Agent shall be entitled to rely upon
advice of counsel concerning legal matters, and upon this Agreement and any
schedule, certificate, statement, report, notice or other writing which it
believes to be genuine or to have been presented by a proper person. Neither the
Administrative Agent nor any of its directors, officers, employees or agents
shall (i) be responsible for any recitals, representations or warranties
contained in, or for the execution, validity, genuineness, effectiveness or
enforceability of, this Agreement or any other instrument or document delivered
hereunder

                                      -37-

<PAGE>   39



or in connection herewith, (ii) be responsible for the validity, genuineness,
perfection, effectiveness, enforceability, existence, value or enforcement of
any collateral security, (iii) be under any duty to inquire into or pass upon
any of the foregoing matters, or to make any inquiry concerning the performance
by the Company or any other obligor of its obligations, or (iv) in any event, be
liable as such for any action taken or omitted by it or them, except for its or
their own gross negligence or willful misconduct. The agency hereby created
shall in no way impair or affect any of the rights and powers of, or impose any
duties or obligations upon, the Administrative Agent in its individual capacity.

     13.4 Credit Investigation. Each Lender acknowledges that it has made such
inquiries and taken such care on its own behalf as would have been the case had
such Lender's Commitment been granted and such Lender's Loans been made directly
by such Lender to the Company without the intervention of the Administrative
Agent or any other Lender. Each Lender agrees and acknowledges that the
Administrative Agent makes no representations or warranties about the
creditworthiness of the Company or any other party to this Agreement or with
respect to the legality, validity, sufficiency or enforceability of this
Agreement or any Note or the value of any security therefor.

     13.5 Administrative Agent and Affiliates. The Administrative Agent in its
individual capacity shall have the same rights and powers hereunder as any other
Lender and may exercise or refrain from exercising the same as though it were
not the Administrative Agent, and the Administrative Agent and its affiliates
may accept deposits from and generally engage in any kind of business with the
Company or any affiliate thereof as if the Administrative Agent were not the
Administrative Agent hereunder.

     13.6 Action on Instructions of the Required Lenders. As to any matters not
expressly provided for by this Agreement (including, without limitation,
enforcement of this Agreement and collection of the Loans), the Administrative
Agent shall not be required to exercise any discretion or take any action, but
the Administrative Agent shall in all cases be fully protected in acting or
refraining from acting upon the written instructions (i) from the Required
Lenders, except for instructions which 

                                      -38-


<PAGE>   40



under the express provisions hereof must be received by the Administrative Agent
from all Lenders, and (ii) in the case of such instructions, from all Lenders.
In no event will the Administrative Agent be required to take any action which
exposes the Administrative Agent to personal liability or which is contrary to
this Agreement or applicable law. The relationship between the Agent and the
Lenders is and shall be that of agent and principal only and nothing herein
contained shall be construed to constitute the Administrative Agent a trustee
for any holder of a Note or of a participation therein nor to impose on the
Administrative Agent duties and obligations other than those expressly provided
for herein.

     13.7 Funding Reliance. (a) Unless the Administrative Agent receives notice
from a Lender by 1:00 p.m., Atlanta time, on the day of a proposed borrowing
that such Lender will not make available to the Administrative Agent the amount
which would constitute its Percentage of such borrowing in accordance with
Section 2.3, the Administrative Agent may assume that such Lender has made such
amount available to the Administrative Agent and, in reliance upon such
assumption, make a corresponding amount available to the Company. If and to the
extent such Lender has not made any such amount available to the Administrative
Agent, such Lender and the Company jointly and severally agree to repay such
amount to the Administrative Agent forthwith on demand, together with interest
thereon (i) in the case of the Company, the interest rate applicable to Loans
comprising such borrowing and (ii) in the case of such Lender, the Federal Funds
Rate (or, beginning on the third Business Day after demand, the rate set forth
in clause (i)). Nothing set forth in this clause (a) shall relieve any Lender of
any obligation it may have to make any Loan hereunder.

         (b) Unless the Administrative Agent receives notice from the Company
prior to the due date for any payment hereunder that the Company does not intend
to make such payment, the Administrative Agent may assume that the Company has
made such payment and, in reliance upon such assumption, make available to each
Lender its share of such payment. If and to the extent that the Company has not
made any such payment to the Administrative Agent, each Lender which received a
share of such payment shall repay such share (or the relevant portion thereof)
to the Administrative Agent forthwith on demand, together with interest 


                                      -39-


<PAGE>   41

thereon at the Federal Funds Rate (or, beginning on the third Business Day after
demand, at the Floating Rate). Nothing set forth in this clause (b) shall
relieve the Company of any obligation it may have to make any payment hereunder.

     13.8  Resignation. The Administrative Agent may resign as such at any time
upon at least 30 days' prior notice to the Company and the Lenders. In the event
of any such resignation, the Required Lenders (with, so long as no Event of
Default or Unmatured Event of Default exists, the consent of the Company, which
consent shall not be unreasonably delayed or withheld) shall as promptly as
practicable appoint a successor Administrative Agent. If no successor shall have
been so appointed, and shall have accepted such appointment, within 30 days
after the giving of notice of such resignation, then the retiring Administrative
Agent may, on behalf of the Lenders, appoint a successor Administrative Agent,
which shall be a commercial bank having a branch in the United States of America
and having a combined capital, surplus and undivided profits of at least
$500,000,000. Upon the acceptance of any appointment as Administrative Agent
hereunder by a successor Administrative Agent, such successor Administrative
Agent shall thereupon succeed to and become vested with all rights, powers,
privileges and duties of the retiring Administrative Agent, and the retiring
Administrative Agent shall be discharged from all further duties and obligations
under this Agreement. After any resignation pursuant to this Section 13.8, the
provisions of this Section 13 shall inure to the benefit of the retiring
Administrative Agent as to any actions taken or omitted to be taken by it while
it was Administrative Agent hereunder.

   SECTION 14 GENERAL.

     14.1  Waiver; Amendments. No delay on the part of the Administrative Agent
or any Lender in the exercise of any right, power or remedy shall operate as a
waiver thereof, nor shall any single or partial exercise by any of them of any
right, power or remedy preclude other or further exercise thereof, or the
exercise of any other right, power or remedy. No amendment, modification or
waiver of, or consent with respect to, any provision of this Agreement or the
Notes shall in any event be effective unless the same shall be in writing and
signed and delivered by the Administrative Agent and signed and delivered by

                                      -40-

<PAGE>   42


Lenders having an aggregate Percentage of not less than the aggregate Percentage
expressly designated herein with respect thereto or, in the absence of such
designation as to any provision of this Agreement or the Notes, by the Required
Lenders, and then any such amendment, modification, waiver or consent shall be
effective only in the specific instance and for the specific purpose for which
given. No amendment, modification, waiver or consent shall (i) extend or
increase the amount of the Commitments, (ii) extend the date for payment of any
principal of or interest on the Loans or any fees payable hereunder, (iii)
reduce the principal amount of any Loan, the rate of interest thereon or any
fees payable hereunder, (iv) change the definition of Required Lenders or
otherwise reduce the aggregate Percentage required to effect an amendment,
modification, waiver or consent or (v) amend this sentence without, in each
case, the consent of all Lenders. No provisions of Section 13 shall be amended,
modified or waived without the written consent of the Administrative Agent.

     14.2 Confirmations. The Company and each holder of a Note agree from time
to time, upon written request received by it from the other, to confirm to the
other in writing (with a copy of each such confirmation to the Administrative
Agent) the aggregate unpaid principal amount of the Loans then outstanding under
such Note.

     14.3 Notices. Except as otherwise provided in Sections 2.3, 2.4 and 4.3,
all notices hereunder shall be in writing (including, without limitation,
facsimile transmission) and shall be sent to the applicable party at its address
shown below its signature hereto or at such other address as such party may, by
written notice received by the other party, have designated as its address for
such purpose. Notices sent by facsimile transmission shall be deemed to have
been given when sent; notices sent by mail shall be deemed to have been given
three Business Days after the date when sent by registered or certified mail,
postage prepaid; and notices sent by hand delivery shall be deemed to have been
given when received. For purposes of Sections 2.3, 2.4 and 4.3, the
Administrative Agent shall be entitled to rely on telephonic instructions from
any person that the Administrative Agent in good faith believes is an authorized
officer or employee of the Company, and the Company shall hold the
Administrative Agent and each Lender harmless from


                                      -41-

<PAGE>   43


any loss, cost or expense resulting from any such reliance.

     14.4 Costs, Expenses and Taxes. The Company agrees to pay on demand all
reasonable out-of-pocket costs and expenses of the Agents and the Co-Arrangers
(including the fees and charges of counsel for the Administrative Agent and of
local counsel, if any, who may be retained by said counsel) in connection with
the preparation, execution, delivery and administration of this Agreement and
all other documents provided for herein or delivered or to be delivered
hereunder or in connection herewith (including, without limitation, any
amendment, supplement or waiver to this Agreement or any such other document).
The Company further agrees to pay all reasonable out-of-pocket costs and
expenses (including reasonable attorneys' fees, court costs and other legal
expenses and allocated costs of staff counsel) incurred by each Agent, each
Co-Arranger and each Lender in connection with (i) the negotiation of any
restructuring or "work-out" (whether or not consummated) of the obligations of
the Company hereunder and (ii) the enforcement of this Agreement or any other
document provided for herein or delivered or to be delivered hereunder or in
connection herewith. In addition, the Company agrees to pay, and to save the
Agents, the Co-Arrangers and the Lenders harmless from all liability for, any
stamp or other similar taxes which may be payable in connection with the
execution and delivery of this Agreement, the borrowings hereunder, the issuance
of the Notes or the execution and delivery of any other document provided for
herein or delivered or to be delivered hereunder or in connection herewith. All
obligations provided for in this Section 14.4 shall survive repayment of the
Loans, cancellation of the Notes and any termination of this Agreement.

     14.5 Successors and Assigns. This Agreement shall be binding upon the
Company, the Lenders and the Administrative Agent and their respective
successors and assigns, and shall inure to the benefit of the Company, the
Lenders and the Administrative Agent and the successors and assigns of the
Lenders and the Administrative Agent. The Company may not assign its rights or
obligations hereunder without the prior written consent of all Lenders.

                                      -42-

<PAGE>   44

     14.6 Assignments; Participations.

     14.6.1 Assignments. Any Lender may, with the prior written consents of the
Company and the Administrative Agent (which consents shall not be unreasonably
delayed or withheld), at any time assign and delegate to one or more commercial
banks or other Persons (any Person to whom such an assignment and delegation is
to be made being herein called an "Assignee"), all or any fraction of such
Lender's Loans and Commitment (which assignment and delegation shall be of a
constant, and not a varying, percentage of all the assigning Lender's Loans and
Commitment) in a minimum aggregate amount equal to the lesser of (i) the
assigning Lender's remaining Commitment and (ii) $5,000,000; provided, however,
that (a) no assignment and delegation may be made to any Person if, at the time
of such assignment and delegation, the Company would be obligated to pay any
greater amount under Section 4.1(b), 7.6 or 8 to the Assignee than the Company
is then obligated to pay to the assigning Lender under such Section and (b) the
Company and the Administrative Agent shall be entitled to continue to deal
solely and directly with such Lender in connection with the interests so
assigned and delegated to an Assignee until the date when all of the following
conditions shall have been met:

                  (x) five Business Days (or such lesser period of time as the
         Administrative Agent and the assigning Lender shall agree) shall have
         passed after written notice of such assignment and delegation, together
         with payment instructions, addresses and related information with
         respect to such Assignee, shall have been given to the Company and the
         Administrative Agent by such assigning Lender and the Assignee,

                  (y) the assigning Lender and the Assignee shall have executed
         and delivered to the Company and the Administrative Agent an assignment
         agreement substantially in the form of Exhibit E (an "Assignment
         Agreement"), together with any documents required to be delivered
         thereunder, which Assignment Agreement shall have been accepted by the
         Administrative Agent and the Company, and

                  (z) the assigning Lender or the Assignee shall have paid the
         Administrative Agent a processing fee of $2,500.


                                      -43-

<PAGE>   45

From and after the date on which the conditions described above have been met,
(x) such Assignee shall be deemed automatically to have become a party hereto
and, to the extent that rights and obligations hereunder have been assigned and
delegated to such Assignee pursuant to such Assignment Agreement, shall have the
rights and obligations of a Lender hereunder, and (y) the assigning Lender, to
the extent that rights and obligations hereunder have been assigned and
delegated by it pursuant to such Assignment Agreement, shall be released from
its obligations hereunder. Within five Business Days after effectiveness of any
assignment and delegation, the Company shall execute and deliver to the
Administrative Agent (for delivery to the Assignee and the Assignor, as
applicable) a new Note in the principal amount of the Assignee's Commitment and,
if the assigning Lender has retained a Commitment hereunder, a replacement Note
in the principal amount of the Commitment retained by the assigning Lender (such
Note to be in exchange for, but not in payment of, the predecessor Note held by
such assigning Lender). Each such Note shall be dated the effective date of such
assignment. The assigning Lender shall mark the predecessor Note "exchanged" and
deliver it to the Company. Accrued interest on that part of the predecessor Note
being assigned shall be paid as provided in the Assignment Agreement. Accrued
interest and fees on that part of the predecessor Note not being assigned shall
be paid to the assigning Lender. Accrued interest and accrued fees shall be paid
at the same time or times provided in the predecessor Note and in this
Agreement. Any attempted assignment and delegation not made in accordance with
this Section 14.6.1 shall be null and void.

     Notwithstanding the foregoing provisions of this Section 14.6.1 or any
other provision of this Agreement, any Lender may at any time assign all or any
portion of its Loans and its Note to a Federal Reserve Bank (but no such
assignment shall release any Lender from any of its obligations hereunder).


     14.6.2  Participations. Any Lender may at any time sell to one or more
commercial banks or other Persons participating interests in any Loan owing to
such Lender, the Note held by such Lender, the Commitment of such Lender or any
other interest of such Lender hereunder (any Person purchasing any such
participating interest being herein called a "Participant"). In the event of a
sale by a Lender of a participating interest to a 


                                      -44-

<PAGE>   46



Participant, (x) such Lender shall remain the holder of its Note for all
purposes of this Agreement and (y) the Company and the Administrative Agent
shall continue to deal solely and directly with such Lender in connection with
such Lender's rights and obligations hereunder. No Participant shall have any
direct or indirect voting rights hereunder (except that a Lender may grant a
Participant rights with respect to any of the events described in the
penultimate sentence of Section 14.1). The Company agrees that if amounts
outstanding under this Agreement and any Note are due and payable (as a result
of acceleration or otherwise), each Participant shall be deemed to have the
right of setoff in respect of its participating interest in amounts owing under
this Agreement and any Note to the same extent as if the amount of its
participating interest were owing directly to it as a Lender under this
Agreement or such Note; provided that such right of setoff shall be subject to
the obligation of each Participant to share with the Lenders, and the Lenders
agree to share with each Participant, as provided in Section 7.5. The Company
also agrees that each Participant shall be entitled to the benefits of Sections
4.1(b), 7.6 and 8 as if it were a Lender (provided that no Participant shall
receive any greater compensation pursuant to such Sections than would have been
paid to the participating Lender if no participation had been sold).

     14.7 Governing Law. This Agreement and each Note shall be a contract made
under and governed by the laws of the State of Illinois applicable to contracts
made and to be performed entirely within the State of Illinois. Whenever
possible each provision of this Agreement shall be interpreted in such manner as
to be effective and valid under applicable law, but if any provision of this
Agreement shall be prohibited by or invalid under applicable law, such provision
shall be ineffective to the extent of such prohibition or invalidity, without
invalidating the remainder of such provision or the remaining provisions of this
Agreement. All obligations of the Company and rights of the Administrative Agent
and the Lenders expressed herein or in the Notes shall be in addition to and not
in limitation of those provided by applicable law.

     14.8 Counterparts; Effectiveness. This Agreement may be executed in any
number of counterparts and by the different parties hereto on separate
counterparts and each such counterpart


                                      -45-

<PAGE>   47


shall be deemed to be an original, but all such counterparts shall together
constitute but one and the same Agreement. When counterparts executed by all of
the parties hereto shall have been lodged with the Administrative Agent (or, in
the case of any Lender as to which an executed counterpart shall not have been
so lodged, the Administrative Agent shall have received confirmation from such
Lender of execution of a counterpart hereof by such Lender), this Agreement
shall become effective as of the date hereof, and at such time the
Administrative Agent shall notify the Company and each Lender.

     14.9 Computations. Where the character or amount of any asset or liability
or item of income or expense is required to be determined, or any consolidation
or other accounting computations is required to be made, for the purpose of this
Agreement, such determination or calculation shall, to the extent applicable and
except as otherwise specified in this Agreement, be made in accordance with
generally accepted accounting principles applied on a basis consistent with
those used in the preparation of the Company's audited financial statements for
the fiscal year of the Company ended December 31, 1995.



                                      -46-

<PAGE>   48



Delivered at Chicago, Illinois, as of the day and year first above written.

                                           ILLINOVA CORPORATION


                                           By______________________________
                                           Title___________________________

                                           Illinova Corporation
                                           500 South 27th Street
                                           Decatur, Illinois  60525
                                           Attention:  Treasurer
                                           Telephone:  217-424-6600
                                           Facsimile:  217-424-6978

                                           With a copy to:

                                           Schiff Hardin & Waite
                                           7200 Sears Tower
                                           233 South Wacker Drive
                                           Attention:  Robert J. Regan
                                           Telephone:  (312) 258-5600
                                           Facsimile:  (312) 258-5606


                                           CIBC INC., individually and
                                              as Administrative Agent


                                           By________________________________
                                           Title_____________________________


                                           CIBC Inc.
                                           425 Lexington Avenue
                                           Syndications, 7th Floor
                                           New York, New York  10017
                                           Attention:  Cynthia Trust
                                           Telephone:  (212) 856-3675
                                           Facsimile:  (212) 856-3763




                                      -47-

<PAGE>   49


                                           With a copy to:

                                           CIBC Inc.
                                           200 West Madison, Suite 2300
                                           Chicago, Illinois  60606
                                           Attention:  Utilities Group
                                           Telephone:  312-855-3252
                                           Facsimile:  312-750-0927


                                           THE FIRST NATIONAL BANK OF CHICAGO


                                           By________________________________
                                           Title_____________________________

                                           The First National Bank of
                                           Chicago
                                           One First National Plaza
                                           Chicago, Illinois  60670
                                           Attention:  Richard H. Waldman
                                           Telephone:  (312) 732-3520
                                           Facsimile:  (312) 732-3055



                                      -48-


<PAGE>   50
                                   SCHEDULE I

                          COMMITMENTS AND PERCENTAGES


<TABLE>
<CAPTION>
Lender                                           Commitment                   Percentage
- ------                                           ----------                   ----------
<S>                                              <C>                             <C>
CIBC Inc.                                        $ 50,000,000                     50%

The First National Bank                          $ 50,000,000                     50%
of Chicago                                       ------------                     -- 
          

                                                 $100,000,000                    100%
                                                                                     
</TABLE>
<PAGE>   51

                                  SCHEDULE II

                                PRICING SCHEDULE


         The Applicable Margin and Non-Use Fee Rate shall be determined based
on the then-current Rating Level as set forth below.


<TABLE>
<CAPTION>
=========================================================================================
                           Rating                  Applicable                 Non-Use Fee
                            Level                   Margin                      Rate
                           -------                 ----------                 -----------
- -----------------------------------------------------------------------------------------
                           <S>                     <C>                        <C>
                           1                       0.550%                     0.150%
- -----------------------------------------------------------------------------------------                           
                           2                       0.650%                     0.175%
- -----------------------------------------------------------------------------------------                           
                           3                       0.875%                     0.200%
- -----------------------------------------------------------------------------------------                           
                           4                       1.250%                     0.250%
========================================================================================== 
</TABLE>
<PAGE>   52

                                   EXHIBIT A

                                    FORM OF
                                      NOTE

$___________                                                   ___________, 199_
                                                               Chicago, Illinois

         FOR VALUE RECEIVED, the undersigned promises to pay to the order of
_________________, at the principal office of CIBC INC. (the "Administrative
Agent"), in New York, New York, on the date set forth in the Credit Agreement
referred to below, ______________________ Dollars ($____________) or, if less,
the aggregate unpaid amount of all Loans made by the payee to the undersigned
pursuant to the Credit Agreement (as shown in the records of the payee or, at
the payee's option, on the schedule attached hereto and any continuation
thereof).

         The undersigned further promises to pay interest on the unpaid
principal amount of each Loan evidenced hereby from the date of such Loan until
such Loan is paid in full, payable at the rate(s) and at the time(s) set forth
in the Credit Agreement.  Payments of both principal and interest are to be
made in lawful money of the United States of America.

         This Note evidences indebtedness incurred under, and is subject to the
terms and provisions of, the Credit Agreement, dated as of June 12, 1996
(herein, as amended or otherwise modified from time to time, called the "Credit
Agreement"; terms not otherwise defined herein are used herein as defined in
the Credit Agreement), among the undersigned, certain financial institutions
(including the payee) and the Administrative Agent, to which Credit Agreement
reference is hereby made for a statement of the terms and provisions under
which this Note may or must be paid prior to its due date or may have its due
date accelerated.

         In addition to and not in limitation of the foregoing and the
provisions of the Credit Agreement, the undersigned further agrees, subject
only to any limitation imposed by applicable law, to pay all reasonable
expenses, including reasonable attorneys' fees and legal expenses, incurred by
the holder of this Note in endeavoring to collect any amounts payable hereunder
which are not paid when due, whether by acceleration or otherwise.  Each of the
Company and each guarantor hereof waives demand, presentment,
<PAGE>   53


protest, diligence, notice of dishonor and any other formality in connection
with this Note.

   This Note is made under and governed by the internal laws of the State of
Illinois.

                                                ILLINOVA CORPORATION



                                                By
                                                   -----------------------------

                                                Title
                                                     ---------------------------





                                      -2-
<PAGE>   54

Schedule Attached to Note dated __________, 199_ of ILLINOVA CORPORATION
payable to the order of ________________________.

<TABLE>
<S>                            <C>                        <C>                   <C>                   <C>
Date and                       Date and
Amount of                      Amount of
Loan or of                     Repayment or of
conversion from                conversion into                                  Unpaid
another type of                another type of            Interest              Principal             Notation
Loan                           Loan                       Period                Balance               Made by
</TABLE>

                            1.  FLOATING RATE LOANS

________________________________________________________________________________

________________________________________________________________________________

________________________________________________________________________________

________________________________________________________________________________

________________________________________________________________________________

________________________________________________________________________________

________________________________________________________________________________

________________________________________________________________________________

________________________________________________________________________________

                             2.  EURODOLLAR LOANS

________________________________________________________________________________

________________________________________________________________________________

________________________________________________________________________________

________________________________________________________________________________

________________________________________________________________________________

________________________________________________________________________________





                                      -3-
<PAGE>   55

________________________________________________________________________________

________________________________________________________________________________

________________________________________________________________________________





                                      -4-
<PAGE>   56

                                   EXHIBIT B

                      SCHEDULE OF SIGNIFICANT SUBSIDIARIES



<TABLE>

                                                                                Percentage
                                                                                Ownership of
                                                                                the Company
Name of Significant                  State of                                   and its
   Subsidiary                        Organization                               Subsidiaries
- -------------------                  ------------                               ------------
<S>                                  <C>                                        <C>
Illinois Power                       Illinois                                   100%
   Company

</TABLE>


<PAGE>   57

                                   EXHIBIT C

                                SCHEDULE OF DEBT


<TABLE>
<CAPTION>
Description of Debt                                                              Amount
- -------------------                                                              ------
<S>                                                                             <C>
Illinois Generating Company equity
guarantee for the Tenaska Washington
Partners II, IPG Frederickson, Inc.
project                                                                         $7,670,000


Illinova Generating Company equity
guarantee for the Tenaska IV Texas
Partners, IGC Brazos, Inc. project                                               4,867,000

Illinova Generating Company equity
guarantee for the Aguaytia energy,
L.L.C., IGC Aguaytia Partners, L.L.C.,
Project                                                                         21,718,000

Illinova letters of credit for the
Tenaska Uch Power Project                                                        4,344,000

Illinova letters of credit for the Tenaska
Uch Power Project                                                               17,619,000

Illinova guarantees for the account
Tenaska Marketing Ventures                                                      23,561,000
                                                              
Tenaska Marketing Ventures hedging
position Mark to Market                                                          5,244,000*
</TABLE>





*  As of June 7, 1996


<PAGE>   58

                                   EXHIBIT D

                   FORM OF OPINION OF COUNSEL FOR THE COMPANY

                                 June __, 1996

CIBC INC.,
  individually and as Administrative
  Agent, and the other financial
  institutions which are parties to
  the Credit Agreement referred to below
200 West Madison
Chicago, Illinois 60606

         Re:     Credit Agreement, dated as of June 12, 1996, with
                 Illinova Corporation

Ladies and Gentlemen:

         We have acted as counsel for Illinova Corporation, an Illinois
corporation (the "Company"), in connection with the execution and delivery of
the Credit Agreement, dated as of June 12, 1996 (the "Credit Agreement"), among
the Company, the financial institutions which are parties thereto (the
"Lenders"), and CIBC Inc., as administrative agent for the Lenders.  We are
rendering this opinion at the request of the Company as required by Section
11.1.5 of the Credit Agreement.  Unless otherwise defined herein, capitalized
terms used herein shall have the respective meanings assigned to such terms in
the Credit Agreement.

         In this connection, we have examined an original or a copy of the
following:

         (a)     The Credit Agreement;

         (b)     The form of Notes to be issued by the Company to each Lender;

         (c)     The Articles of Incorporation and By-Laws of the Company; and

         (d)     Resolutions adopted at a meeting of the Board of Directors of
                 the Company on June 11, 1996 (the "Resolutions"), certified by
                 the Secretary of the
<PAGE>   59


                Company.

         We have examined such other records, documents, proceedings and
certificates of officers and representatives of the Company and made such other
examinations as we have deemed necessary in order to enable us to give the
opinions hereinafter contained.

         For purposes of this opinion, we have assumed (a) the genuineness of
the signatures, and the authority, of persons signing all documents in
connection with which this opinion is rendered on behalf of parties other than
the Company, (b) the authenticity of all documents submitted to us as
originals, (c) the conformity to authentic original documents of all documents
submitted to us as certified or photostatic copies, and (d) that the Credit
Agreement is the legal, valid and binding obligation of the parties thereto
other than the Company.

         Based upon and subject to the foregoing, and subject to the
qualifications set forth below, we are of the opinion that:

         (1)     The Company and Illinois Power Company are corporations duly
incorporated, validly existing and in good standing under the laws of
the jurisdiction of their respective incorporation.

         (2)     The Company has full corporate power to execute, deliver and
perform the Credit Agreement and the Notes, to borrow moneys under the Credit
Agreement, and to perform its obligations under the Credit Agreement and the
Notes.

         (3)     The execution and delivery of the Credit Agreement and the
Notes and the borrowing of Loans under the Credit Agreement, and the
performance by the Company of its obligations under the Credit Agreement and
the Notes have been duly authorized by all necessary corporate action, have
received all necessary governmental and regulatory approval, and do not and
will not violate, or result in the creation or imposition of a Lien under, any
provision of law or of the Articles of Incorporation or By-Laws of the Company
or, to our knowledge, of any agreement, instrument, order or decree that is
binding upon the Company.

         (4)     The Credit Agreement has been duly executed and delivered by 
the Company, and the Credit Agreement is, and the Notes, when duly executed and
delivered by the Company will be,
        


                                      -2-


<PAGE>   60

legal, valid and binding obligations of the Company, enforceable in accordance
with their terms.

         Our opinion is subject to the following qualifications:

         (a)  We express no opinion as to the effect of the law of any
jurisdiction other than the State of Illinois.

         (b)  We express no opinion with respect to the rights of any
Participant under Section 7.4 of the Credit Agreement.

         (c)  Our opinion in paragraph (4) above is subject to the effect of any
applicable bankruptcy, insolvency, reorganization, moratorium or similar law
affecting creditors' rights generally and to the effect of general principles
of equity (regardless of whether considered in a proceeding in equity or at
law), including, without limitation, concepts of materiality, reasonableness,
good faith and fair dealing.

         (d)  We express no opinion with respect to indemnification or
contribution obligations which contravene public policy.

         We are members of the bar of the State of Illinois, and the foregoing
opinion is limited to the laws of the State of Illinois and the Federal law of
the United States of America.

                                                               Very truly yours,





                                       -3-
<PAGE>   61

                                   EXHIBIT E

                                    FORM OF
                              ASSIGNMENT AGREEMENT

                                                          Date: ______________  

To:      Illinova Corporation

                  and

         CIBC Inc.,  as Administrative Agent

Re:  Assignment under the Credit Agreement referred to below

Gentlemen and Ladies:

         We refer to Section 14.6.1 of the Credit Agreement dated as of June
12, 1996 (as amended or otherwise modified, the "Credit Agreement") among
Illinova Corporation (the "Company"), various financial institutions and CIBC
Inc., as administrative agent (the "Administrative Agent").  Unless otherwise
defined herein or the context otherwise requires, terms used herein have the
meanings provided in the Credit Agreement.

          _____________________ (the "Assignor") hereby sells and assigns to
______________ (the "Assignee"), and the Assignee hereby purchases and assumes
from the Assignor, that interest in and to the Assignor's rights and
obligations under the Credit Agreement as of the date hereof equal to ____% of
all of the Loans and Commitments, such sale, purchase, assignment and
assumption to be effective as of ______________, 199__, or such later date on
which the Company and the Administrative Agent shall have consented hereto (the
"Effective Date").  After giving effect to such sale, purchase, assignment and
assumption, the Assignee's Percentage for purposes of the Credit Agreement will
be as set forth opposite the Assignee's name on the signature pages hereof.

         The Assignor hereby instructs the Administrative Agent to make all
payments from and after the Effective Date in respect of the interest assigned
hereby directly to the Assignee.  The Assignor and the Assignee agree that all
interest and fees accrued up to, but not including, the Effective Date are the
property of the Assignor, and not the Assignee.  The Assignee


<PAGE>   62


agrees that, upon receipt of any such interest or fees, the Assignee will
promptly remit the same to the Assignor.

         The Assignee hereby confirms that it has received a copy of the Credit
Agreement and the exhibits related thereto, together with copies of the
documents which were required to be delivered under the Credit Agreement as a
condition to the making of the initial Loans thereunder.  The Assignee
acknowledges and agrees that it (i) has made and will continue to make such
inquiries and has taken and will take such care on its own behalf as would have
been the case had its Commitment been granted and its Loans been made directly
by the Assignee to the Company without the intervention of the Administrative
Agent, the Assignor or any other Lender and (ii) has made and will continue to
make, independently and without reliance upon the Administrative Agent, the
Assignor or any other Lender and based on such documents and information as it
has deemed appropriate, its own credit analysis and decisions relating to the
Credit Agreement.  The Assignee further acknowledges and agrees that neither
the Administrative Agent nor the Assignor has made any representation or
warranty about the creditworthiness of the Company or any other party to the
Credit Agreement or with respect to the legality, validity, sufficiency or
enforceability of the Credit Agreement or any Note or the value of any security
therefor.  This assignment shall be made without recourse to the Assignor.

         The Assignor represents and warrants that it is the legal and
beneficial owner of the interest being assigned by it hereunder and that such
interest is free and clear of any adverse claim.

         The Assignee represents and warrants to the Company and the
Administrative Agent that, as of the date hereof, the Company will not be
obligated to pay any greater amount under Section 7.6 or 8.1 of the Credit
Agreement than the Company is obligated to pay to the Assignor under such
Section.

         Except as otherwise provided in the Credit Agreement, effective as of
the Effective Date:

         (a)     the Assignee (i) shall be deemed automatically to have become
                 a party to the Credit Agreement and have all the rights and
                 obligations of a "Lender" under the Credit





                                       -2-
<PAGE>   63


                Agreement as if it were an original signatory thereto to the
                extent specified in the second paragraph hereof; and (ii)
                agrees to be bound by the terms and conditions set forth in the
                Credit Agreement as if it were an original signatory thereto;
                and

         (b)    the Assignor shall be released from its obligations under the
                Credit Agreement to the extent specified in the second
                paragraph hereof.

         The Assignor and the Assignee hereby agree that the [Assignor]
[Assignee] will pay to the Administrative Agent the processing fee referred to
in Section 14.6 of the Credit Agreement.  The payment of the processing fee
shall be a condition to the effectiveness of this assignment.

         The Assignee hereby advises each of you of the following
administrative details with respect to the assigned Loans and Commitment:

         (A)     Address for Notices:

                 Institution Name:

                 Address:



                 Attention:

                 Telephone:

                 Facsimile:

         (B)     Payment Instructions:

         Please evidence your receipt hereof and consent to the sale,
assignment, purchase and assumption set forth herein by signing and returning
counterparts hereof to the Assignor and the Assignee.


Percentage =    %                                         [ASSIGNEE]
             ---
                                      -3-





<PAGE>   64



                 By:  
                    ---------------------
   

                 Title: 

                                   [ASSIGNOR]


                 By:  
                    --------------------
                                      Title:


ACKNOWLEDGED AND CONSENTED TO
this ____ day of ________, 199_

CIBC INC., as Administrative Agent


By:
   ----------------------------------   
   Title:
         ----------------------------


ACKNOWLEDGED AND CONSENTED TO
this ___ day of _____________, 199__

ILLINOVA CORPORATION



By:
   ----------------------------------
   Title:
         ----------------------------

                                      -4-





<PAGE>   65

                                   EXHIBIT F

                           COMPLIANCE (SECTION 9.15)



                                      NONE
<PAGE>   66

                                   EXHIBIT G

                             LIENS (SECTION 10.14)



                                      NONE
<PAGE>   67

                                   EXHIBIT H

                  SECTION 9 OF ILLINOIS POWER CREDIT AGREEMENT
<PAGE>   68

                               TABLE OF CONTENTS

<TABLE>
<CAPTION>
                                                                                                              PAGE
                                                                                                              ----
<S>                                                                                                           <C>
SECTION 1             DEFINITIONS   . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
                                                                                                               
         1.1          Definitions   . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
         1.2          Computations  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
         1.3          Cross-References; Section Captions  . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
                                                                                                               
SECTION 2             COMMITMENTS OF THE LENDERS; TYPES OF LOANS; BORROWING AND CONVERSION PROCEDURES.  . . . . 8
         2.1          Commitments   . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
         2.2          Various Types of Loans  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
         2.3          Borrowing Procedures  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
         2.4          Conversion Procedures   . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
         2.5          Warranty upon Conversion  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
         2.6          Conditions  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
         2.7          Pro Rata Treatment  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
         2.8          Commitments Several   . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
                                                                                                               
SECTION 3             NOTES EVIDENCING LOANS  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10
         3.1          Notes   . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10
         3.2          Recordkeeping   . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10
                                                                                                               
SECTION 4             INTEREST  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10
         4.1          Interest Rates  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10
         4.2          Interest Payment Dates  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11
         4.3          Interest Periods  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11
         4.4          Setting and Notice of Eurodollar Rates  . . . . . . . . . . . . . . . . . . . . . . . . .12
         4.5          Computation of Interest   . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .12
                                                                                                               
SECTION 5             FEES  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .12
         5.1          Non-Use Fee   . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .12
         5.2          Administrative Agent's Fees   . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .12
                                                                                                               
SECTION 6             REDUCTION OR TERMINATION OF THE COMMITMENTS;                                             
                      PREPAYMENTS   . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .13
         6.1          Reduction or Termination of the Commitments   . . . . . . . . . . . . . . . . . . . . . .13
         6.2          Prepayments   . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .13
                                                                                                               
SECTION 7             MAKING AND PRORATION OF PAYMENTS; SETOFF; TAXES   . . . . . . . . . . . . . . . . . . . .13

</TABLE>
                                      -i-





<PAGE>   69

                               TABLE OF CONTENTS
                                  (CONTINUED)

<TABLE>
<CAPTION>
                                                                                                               PAGE
                                                                                                               ----
         <S>                                                                                                   <C>
         7.1          Making of Payments  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .13
         7.2          Application of Certain Payments   . . . . . . . . . . . . . . . . . . . . . . . . . . . .14
         7.3          Due Date Extension  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14
         7.4          Setoff  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14
         7.5          Proration of Payments   . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14
         7.6          Payments Net of Taxes   . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14

SECTION 8             INCREASED COSTS; SPECIAL PROVISIONS FOR EURODOLLAR LOANS. . . . . . . . . . . . . . . . .15
         8.1          Increased Costs   . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .15
         8.2          Basis for Determining Interest Rate Inadequate or Unfair  . . . . . . . . . . . . . . . .17
         8.3          Changes in Law Rendering Eurodollar Loans Unlawful. . . . . . . . . . . . . . . . . . . .17
         8.4          Funding Losses  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18
         8.5          Right of Lenders to Fund through Other Offices  . . . . . . . . . . . . . . . . . . . . .18
         8.6          Discretion of Lenders as to Manner of Funding   . . . . . . . . . . . . . . . . . . . . .18
         8.7          Mitigation of Circumstances; Replacement of Affected Lender . . . . . . . . . . . . . . .19
         8.8          Conclusiveness of Statements; Survival of Provisions  . . . . . . . . . . . . . . . . . .19
                                                                                                          
SECTION 9             WARRANTIES  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .20
         9.1          Organization, etc   . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .20
         9.2          Authorization; No Conflict  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .20
         9.3          Validity and Binding Nature   . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .20
         9.4          Financial Statements  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .20
         9.5          Conduct of Business   . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .20
         9.6          Litigation and Contingent Liabilities   . . . . . . . . . . . . . . . . . . . . . . . . .21
         9.7          Liens   . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .21
         9.8          Subsidiaries  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .21
         9.9          Employee Benefit Plans  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .21
         9.10         Investment Company Act  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .21
         9.11         Public Utility Holding Company Act  . . . . . . . . . . . . . . . . . . . . . . . . . . .22
         9.12         Regulation U  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22
         9.13         Debt  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22
         9.14         Taxes   . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22
         9.15         Compliance with Laws  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22
</TABLE>                                     

                                      -ii-





<PAGE>   70

                               TABLE OF CONTENTS
                                  (CONTINUED)
<TABLE>    
<CAPTION>
                                                                                                              PAGE
                                                                                                              ----
<S>                   <C>                                                                                      <C>
SECTION 10            COVENANTS   . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22
                                                                                                               
         10.1         Reports, Certificates and Other Information   . . . . . . . . . . . . . . . . . . . . . .22
                      10.1.1        Annual Report . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22
                      10.1.2        Interim Reports . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .23
                      10.1.3        Certificates  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .23
                      10.1.4        Reports to SEC and to Shareholders  . . . . . . . . . . . . . . . . . . . .23
                      10.1.5        Notice of Default and ERISA Matters . . . . . . . . . . . . . . . . . . . .23
                      10.1.6        Significant Subsidiaries  . . . . . . . . . . . . . . . . . . . . . . . . .24
                      10.1.7        Other Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . .24
         10.2         Books, Records, and Inspections   . . . . . . . . . . . . . . . . . . . . . . . . . . . .24
         10.3         Insurance   . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .24
         10.4         Taxes and Liabilities   . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .24
         10.5         Mergers, Consolidations, Sales  . . . . . . . . . . . . . . . . . . . . . . . . . . . . .24
         10.6         Maintenance of Properties   . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .24
         10.7         Conduct of Business   . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .25
         10.8         Employee Benefit Plans  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .25
         10.9         Use of Proceeds   . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .25
         10.10        Other Agreements  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .25
         10.11        Restrictions on Debt  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .25
         10.12        Illinois Power  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .25
         10.13        Compliance with Laws  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .26
         10.14        Limitation on Liens   . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .26
         10.15        Illinova Net Worth  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .27
         10.16        Illinois Power Stock Repurchase Capacity  . . . . . . . . . . . . . . . . . . . . . . . .27
                                                                                                               
SECTION 11            CONDITIONS OF LENDING   . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .27
         11.1         Initial Loan  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .27
                      11.1.1        Notes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .27
                      11.1.2        Resolutions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .27
                      11.1.3        Consents, etc . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .28
                      11.1.4        Incumbency and Signature Certificates . . . . . . . . . . . . . . . . . . .28
                      11.1.5        Opinion of Counsel for the Company  . . . . . . . . . . . . . . . . . . . .28
                      11.1.6        Other . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .28
         11.2         All Loans   . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .28
                      11.2.1        No Default  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .28
                      11.2.2          . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .28

</TABLE>
                                     -iii-





<PAGE>   71
                               TABLE OF CONTENTS
                                  (CONTINUED)
<TABLE>
<CAPTION>
                                                                                                              PAGE
                                                                                                              ----
<S>                   <C>                                                                                     <C> 
SECTION 12            EVENTS OF DEFAULT AND THEIR EFFECT  . . . . . . . . . . . . . . . . . . . . . . . . . . .28
         12.1         Events of Default   . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .28
                      12.1.1        Non-Payment of the Loans, etc.  . . . . . . . . . . . . . . . . . . . . . .29
                      12.1.2        Non-Payment of Other Debt . . . . . . . . . . . . . . . . . . . . . . . . .29
                      12.1.3        Warranties  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .29
                      12.1.4        Bankruptcy, Insolvency, etc . . . . . . . . . . . . . . . . . . . . . . . .29
                      12.1.5        Non-Compliance with Provisions of this Agreement  . . . . . . . . . . . . .30
                      12.1.6        Employee Benefit Plans  . . . . . . . . . . . . . . . . . . . . . . . . . .30
                      12.1.7        Ownership of Significant Subsidiaries . . . . . . . . . . . . . . . . . . .30
                      12.1.8        Judgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .30
                      12.1.9        Change in Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . .30
                      12.1.10       Environmental . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .31
         12.2         Effect of Event of Default  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .31
                                                                                                               
SECTION 13            THE ADMINISTRATIVE AGENT  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .31
         13.1         Authorization   . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .31
         13.2         Indemnification   . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .31
         13.3         Exculpation   . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .32
         13.4         Credit Investigation  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .32
         13.5         Administrative Agent and Affiliates   . . . . . . . . . . . . . . . . . . . . . . . . . .32
         13.6         Action on Instructions of the Required Lenders  . . . . . . . . . . . . . . . . . . . . .33
         13.7         Funding Reliance  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .33
         13.8         Resignation   . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .34
                                                                                                               
SECTION 14            GENERAL   . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .34
         14.1         Waiver; Amendments  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .34
         14.2         Confirmations   . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35
         14.3         Notices   . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35
         14.4         Costs, Expenses and Taxes   . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35
         14.5         Successors and Assigns  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .36
         14.6         Assignments; Participations   . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .36
                      14.6.1        Assignments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .36
                      14.6.2        Participations  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .38
         14.7         Governing Law   . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .38
         14.8         Counterparts  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .39
</TABLE>
                                      -iv-





<PAGE>   72

<TABLE>
<S>                   <C>
SCHEDULE I            Commitments and Percentages
SCHEDULE II           Pricing Schedule
EXHIBIT A             Form of Note  (Section 3.1)
EXHIBIT B             Schedule of Significant Subsidiaries  (Section 9.8)
EXHIBIT C             Schedule of Debt (Section 9.13)
EXHIBIT D             Form of Opinion of Counsel for the Company
                        (Section 11.1.5)
EXHIBIT E             Form of Assignment Agreement  (Section 14.6.1)
EXHIBIT F             Compliance (Section 9.15)
EXHIBIT G             Liens (Section 10.14)
EXHIBIT H             Illinois Power Credit Agreement (Section 10.12)

</TABLE>
                                      -v-





<PAGE>   73



                                FIRST AMENDMENT

                           Dated as of June 28, 1996


         THIS FIRST AMENDMENT dated as of June 28, 1996 amends the Credit
Agreement dated as of June 12, 1996 (the "Credit Agreement") among ILLINOVA
CORPORATION (the "Company"), various financial institutions and CIBC INC., as
Administrative Agent (the "Administrative Agent").  Terms defined in the Credit
Agreement are, unless otherwise defined herein or the context otherwise
requires, used herein as defined therein.

         WHEREAS, the Company, the Administrative Agent and the Lenders have
entered into the Credit Agreement which provides for the Lenders to make Loans
to the Company from time to time; and

         WHEREAS, the parties hereto desire to amend the Credit Agreement in
certain respects as hereinafter set forth;

         NOW, THEREFORE, in consideration of the premises and for other good
and valuable consideration (the receipt and sufficiency of which are hereby
acknowledged), the parties hereto agree as follows:

         SECTION 15  AMENDMENTS.  Effective on (and subject to the occurrence
of) the First Amendment Effective Date (as defined below), the Credit Agreement
shall be amended in accordance with Sections 1.1 through 1.3 below.

         15.1 Addition of Lenders.  The Credit Agreement is amended to include
each of Bank of America Illinois, The First National Bank of Boston, Bank of
Montreal, The Fuji Bank, Limited, ABN AMRO Bank N.V., The Bank of New York and
Deutsche Bank A.G. (collectively, the "Purchasing Lenders" and each
individually a "Purchasing Lender") as a party to the Credit Agreement, as
amended hereby (as so amended, the "Amended Credit Agreement"), and each such
entity shall have all rights and obligations of a Lender under the Amended
Credit Agreement.
        

        


<PAGE>   74


         15.2 Section 2.1.  Section 2.1 of the Credit Agreement is amended by
deleting the amount "$100,000,000" therein and substituting therefor the amount
"$150,000,000".

         15.3 Section 9.8.  Section 9.8 of the Credit Agreement is amended by
deleting the language "free and clear of any Lien" at the end of such Section.

         15.4 Section 11.2.1.  The parenthetical in clause (b) of Section
11.2.1 of the Credit Agreement is amended in its entirety to read as follows:

         (excluding (i) the second sentence of Section 9.6 and (ii) the first
         sentence of Section 9.8)

         15.5 Section 12.1.7.  Section 12.1.7 of the Credit Agreement is
amended in its entirety to read as follows:

                      12.1.7  Ownership of Significant Subsidiaries.  The
         Company shall fail at any time to own, directly or indirectly, all of
         the capital stock of each Subsidiary which is at any time a
         Significant Subsidiary.

         15.6 Schedule I.  Schedule I of the Credit Agreement is amended in its
entirety to read in the form of Schedule I attached hereto.

         SECTION 16   ASSIGNMENTS.  In furtherance of the amendments set forth
in Sections 1.1 and 1.3, on the First Amendment Effective Date each of CIBC
Inc. and The First National Bank of Chicago (collectively, the "Assigning
Lenders") shall sell assignments to the Purchasing Lenders, and each of the
Purchasing Lenders shall purchase assignments from each of the Assigning
Lenders, so that, after giving effect to such purchases and sales, each Lender
will have a pro rata share (according to its Percentage, after giving effect to
Section 1.6) of all Types of Loans.  All payments shall be made in immediately
available funds by the Purchasing Lenders to the Administrative Agent for the
account of the Assigning Lenders at the office of the Administrative Agent in
New York not later than 1:00 p.m., New York time, on the First Amendment
Effective Date.  The

                                      -2-





<PAGE>   75


Administrative Agent shall promptly remit to each Assigning Lender its
share of all such payments.

         SECTION 17  REPRESENTATIONS AND WARRANTIES.  The Company represents
and warrants to the Administrative Agent and the Lenders that (a) each warranty
set forth in Section 9 of the Amended Credit Agreement is true and correct as   
on the date hereof, (b) the execution and delivery by the Company of this First
Amendment and the New Notes (as defined below) and the performance by the
Company of its obligations under the Amended Credit Agreement and the New Notes
(i) are within the corporate powers of the Company, (ii) have been duly
authorized by all necessary corporate action, (iii) have received all necessary
governmental approvals and (iv) do not and will not contravene or conflict with
any provision of law or of the articles of incorporation or by-laws of the
Company or of any indenture, loan agreement or other contract, order or decree
which is binding upon the Company and (c) each of the Amended Credit Agreement
and each New Note is the legal, valid and binding obligation of the Company,
enforceable against the Company in accordance with its terms.

         SECTION 18  EFFECTIVENESS.  The amendments and assignments set forth in
Sections 1 and 2 above shall become effective, as of the day and year first
above written, on such date (the "First Amendment Effective Date") which is the
later to occur of (i) June 28, 1996 and (ii) the date on which the
Administrative Agent shall have received (a) counterparts of this First
Amendment executed by all of the parties hereto and (b) each of the following
documents in form and substance satisfactory to the Administrative Agent:

                      18.1  New Notes.  Promissory notes (the "New Notes") of
         the Company, in the form of Exhibit A to the Credit Agreement, payable
         to the order of the Lenders in the amount of their respective
         Commitments after giving effect hereto.

                      18.2  Resolutions.  Certified copies of resolutions of the
         Board of Directors of the Company authorizing the execution and
         delivery by the Company of this First Amendment and the New Notes and
         the performance by the

                                      -3-





<PAGE>   76


         Company of this First Amendment, the Amended Credit Agreement and the
         New Notes.

                      18.3  Incumbency and Signature Certificates.  A
         certificate of the Secretary or an Assistant Secretary of the Company
         certifying the names of the officer or officers of the Company
         authorized to sign this First Amendment, the New Notes and any other
         document to be executed pursuant to this First Amendment or the
         Amended Credit Agreement, together with a sample of the true signature
         of each such officer (it being understood that the Administrative
         Agent and each Lender may conclusively rely on each such certificate
         until formally advised by a like certificate of any changes therein).

                      18.4  Opinion of Counsel for the Company.  The opinion of
         Schiff Hardin & Waite, counsel to the Company, substantially in the
         form of Exhibit A.

                      18.5  Other.  Such other documents as the Administrative
         Agent or any Lender may reasonably request.

         SECTION 19 MISCELLANEOUS.

         19.1 Continuing Effectiveness, etc.  As herein amended, the Credit 
Agreement shall remain in full force and effect and is  atified and confirmed in
all respects.  After the First Amendment Effective Date, all references in the
Credit Agreement and the New Notes to "Credit Agreement", "Agreement" or similar
terms shall refer to the Amended Credit Agreement.

         19.2 Counterparts.  This First Amendment may be executed in any 
number of counterparts and by the different parties on separate counterparts,
and each such counterpart shall be deemed to be an original but all such
counterparts shall together constitute one and the same First Amendment.
        
         19.3 Governing Law.  This First Amendment shall be a contract made
under and governed by the internal laws of the State of Illinois.

                                      -4-





<PAGE>   77


         19.4 Successors and Assigns.  This First Amendment shall be binding
upon the Company, the Lenders and the Administrative Agent and their respective
successors and assigns, and shall inure to the benefit of the Company, the
Lenders and the Administrative Agent and the respective successors and assigns
of the Administrative Agent and the Lenders.

         19.5 New Lenders.  On the First Amendment Effective Date each of Bank
of America Illinois, The First National Bank of Boston, Bank of Montreal, The
Fuji Bank, Limited, ABN AMRO Bank N.V., The Bank of New York and Deutsche Bank
A.G. shall become a party to the Amended Credit Agreement as fully as if it
were named as a "Lender" thereunder, shall assume all of the rights and
obligations of a Lender under the Amended Credit Agreement, and shall be
governed by the terms and provisions of the Amended Credit Agreement.

         19.6 Return of Old Notes.  As promptly as practicable after the First
Amendment Effective Date, each Assigning Lender shall return to the Company the
notes previously issued to such Assigning Lender under the Credit Agreement
marked to show that such notes have been superseded.

                                      -5-





<PAGE>   78

         Delivered at Chicago, Illinois, as of the day and year first above
written.

                                              ILLINOVA CORPORATION



                                              By
                                                ----------------------------
                                              Title
                                                   -------------------------



                                              CIBC INC., as Administrative Agent



                                              By
                                                -----------------------------
                                              Title
                                                   --------------------------



                                              THE FIRST NATIONAL BANK OF CHICAGO



                                              By
                                                ----------------------------
                                              Title
                                                  --------------------------



                                              BANK OF AMERICA ILLINOIS



                                              By
                                                -----------------------------
                                              Title
                                                   --------------------------


                                      -6-





<PAGE>   79


                                              THE FIRST NATIONAL BANK OF BOSTON


                                              
                                              By
                                                -----------------------------
                                              Title
                                                   --------------------------
                                              
                                              
                                              
                                              
                                              BANK OF MONTREAL




                                              By
                                                -----------------------------
                                              Title
                                                   --------------------------
                                              


                                              THE FUJI BANK, LIMITED



                                              By
                                                -----------------------------
                                              Title
                                                   --------------------------
                                              
                                              


                                              ABN AMRO BANK N.V. CHICAGO BRANCH

                                              By:  ABN AMRO NORTH AMERICA, INC.,
                                                   its agent




                                              By
                                                -----------------------------
                                              Title
                                                   --------------------------




                                              THE BANK OF NEW YORK

                                      -7-





<PAGE>   80





                                              By
                                                -----------------------------
                                              Title
                                                   --------------------------  


                                      -8-







<PAGE>   81






                                              DEUTSCHE BANK A.G.

                                              
                                              By
                                                -----------------------------
                                              Title
                                                   --------------------------  





                                      -9-





<PAGE>   82






                                   SCHEDULE I

                          COMMITMENTS AND PERCENTAGES


<TABLE>
<CAPTION>
Lender                                           Commitment       Percentage
- ------                                           ----------       ----------
<S>                                              <C>              <C>
CIBC Inc.                                        $ 23,000,000     15.333333333%

The First National Bank                          $ 23,000,000     15.333333333%
of Chicago

Bank of America Illinois                         $ 17,000,000     11.333333333%

The First National Bank                          $ 17,000,000     11.333333333%
of Boston

Bank of Montreal                                 $ 17,000,000     11.333333333%

The Fuji Bank, Limited                           $ 17,000,000     11.333333333%

ABN AMRO Bank N.V.                               $ 12,000,000     8.000000000%

The Bank of New York                             $ 12,000,000     8.000000000%

Deutsche Bank A.G.                               $ 12,000,000     8.000000000%
                                                 ------------     ------------

                                                 $150,000,000        100%
</TABLE>





<PAGE>   83

                                   EXHIBIT A

                                FORM OF OPINION





                                                              


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