ATLANTIC RICHFIELD CO /DE
SC 14D1/A, 1995-10-10
PETROLEUM REFINING
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<PAGE>
 
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                      SECURITIES AND EXCHANGE COMMISSION
                            WASHINGTON, D.C. 20549
 
                                SCHEDULE 14D-1
            TENDER OFFER STATEMENT PURSUANT TO SECTION 14(d)(1) 
                   OF THE SECURITIES EXCHANGE ACT OF 1934
                               (AMENDMENT NO. 8)
 
                                ARAN ENERGY plc
                           (NAME OF SUBJECT COMPANY)
 
                           ARCO IRISH HOLDINGS INC.
                          ATLANTIC RICHFIELD COMPANY
                                   (BIDDER)
 
                       ORDINARY SHARES OF IR20p EACH AND
       AMERICAN DEPOSITARY SHARES, EACH REPRESENTING 30 ORDINARY SHARES
                        (TITLE OF CLASS OF SECURITIES)
 
                                  038-528-105
                     (CUSIP NUMBER OF CLASS OF SECURITIES)
 
 
                                 DIANE A. WARD
                          ATLANTIC RICHFIELD COMPANY
                            515 SOUTH FLOWER STREET
                         LOS ANGELES, CALIFORNIA 90071
                                (213) 486-2808
 
          (NAME, ADDRESS, AND TELEPHONE NUMBER OF PERSON AUTHORIZED 
          TO RECEIVE NOTICES AND COMMUNICATIONS ON BEHALF OF BIDDER)
 
                           CALCULATION OF FILING FEE
 
<TABLE>
<CAPTION>
             TRANSACTION VALUATION*                            AMOUNT OF FILING FEE
             ----------------------                            --------------------
             <S>                                               <C>
                  $293,987,494                                       $58,800
</TABLE>
 
*   For purposes of calculating the filing fee pursuant to Regulation 
    (S)240.0-11(d), the transaction valuation is based upon the purchase of 
    261,741,729 Ordinary Shares of IR20p each (including Ordinary Shares 
    represented by American Depositary Shares) plus, assuming the exercise of 
    outstanding options, an additional 12,408,271 Ordinary Shares at IR68p per 
    share for cash and the multiplication of such aggregate purchase price by 
    the currency exchange rate of IR(Pounds)1=US$1.577 (such currency exchange 
    rate being derived from the Financial Times dated August 24, 1995).
 
[X] 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.
 
<TABLE>
   <C>                                 <S>
   Amount Previously Paid:             $52,060
   Form or Registration No.:           Schedule 14D-1
   Filing Party:                       ARCO Irish Holdings Inc. and Atlantic Richfield Company
   Date Filed:                         August 25, 1995
</TABLE>
 
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<PAGE>
 
  This amends and supplements the Tender Offer Statement on Schedule 14D-1 of
ARCO Irish Holdings Inc. ("ARCO Irish Holdings") and Atlantic Richfield
Company ("ARCO"), both corporations incorporated under the laws of Delaware,
initially filed with the Securities and Exchange Commission (the "Commission")
on August 25, 1995, as amended by Amendment Nos. 1, 2, 3, 4, 5, 6 and 7
thereto filed on September 8, 1995, September 14, 1995, September 20, 1995,
September 25, 1995, October 2, 1995, October 3, 1995 and October 4, 1995
(collectively, the "Schedule 14D-1"), with respect to the Offer by N M
Rothschild & Sons Limited on behalf of ARCO Irish Holdings, a wholly owned
subsidiary of ARCO, to acquire the entire share capital of Aran Energy plc,
including all American Depositary Shares.
 
ITEM 1. SECURITY AND SUBJECT COMPANY.
 
  Item 1(b) is amended by adding the following paragraphs:
 
    On October 9, 1995, ARCO and ARCO Irish Holdings increased the
  consideration under the Offer to (i) IR68p per Aran Ordinary Share and
  IR(Pounds)20.40 per Aran ADS if the Statoil/Connemara proposal described in
  the Final Offer Document (as hereinafter defined) is voted down or (ii)
  IR66p per Aran Ordinary Share and IR(Pounds)19.80 per Aran ADS if the
  Statoil/Connemara proposal is approved.
 
    Information concerning the number of outstanding Ordinary Shares and ADSs
  is set forth under the caption "Bases of Calculation and Sources of
  Information" in Appendix 3 to the Final Offer Document and is incorporated
  herein by reference.
 
  Item 1(c) is amended by adding the following sentence:
 
    The information set forth under the caption "Market Price Data and
  Principal Purchases" in Appendix 2 to the Final Offer Document is
  incorporated herein by reference.
 
ITEM 3. PAST CONTACTS, TRANSACTIONS OR NEGOTIATIONS WITH THE SUBJECT COMPANY.
 
  Item 3(b) is amended by adding the following sentence:
 
    The information set forth under the caption "General" in Appendix 2 to
  the Final Offer Document is incorporated herein by reference.
 
ITEM 4. SOURCE AND AMOUNT OF FUNDS OR OTHER CONSIDERATION.
 
  Item 4(a) is amended by adding the following sentence:
 
    The information set forth under the caption "Amount and Source of Funds"
  in Appendix 2 to the Final Offer Document is incorporated herein by
  reference.
 
ITEM 5. PURPOSE OF THE TENDER OFFER AND PLANS OR PROPOSALS OF THE BIDDER.
 
  Item 5 is amended by adding the following sentence:
 
    The information set forth in the letter from the Chairman of ARCO Irish
  Holdings in the Final Offer Document and in the Form of Proxy for use in
  connection with the Aran Extraordinary General Meeting convened for October
  23, 1995 is incorporated herein by reference.
 
ITEM 6. INTEREST IN SECURITIES OF THE SUBJECT COMPANY.
 
  Items 6(a) and (b) are amended by adding the following sentence:
 
    The information set forth under the caption "General" in Appendix 2 to
  the Final Offer Document is incorporated herein by reference.
 
                                       1
<PAGE>
 
ITEM 7. CONTRACTS, ARRANGEMENTS, UNDERSTANDINGS OR RELATIONSHIPS WITH RESPECT
        TO THE SUBJECT COMPANY'S SECURITIES.
 
  Item 7 is amended by adding the following sentence:
 
    The information set forth in the letter from the Chairman of ARCO Irish
  Holdings in the Final Offer Document and in the Form of Proxy for use in
  connection with the Aran Extraordinary General Meeting convened for October
  23, 1995 is incorporated herein by reference.
 
ITEM 10. ADDITIONAL INFORMATION.
 
  Item 10(f) is amended by adding the following sentence:
 
    The information set forth in the Final Cash Offer for Aran Energy plc
  dated October 9, 1995 (the "Final Offer Document") (a copy of which is
  filed as Exhibit (a)(17) hereto), the Disclosure Document dated October 9,
  1995 (a copy of which is filed as Exhibit (a)(18) hereto), the Revised
  Letter of Transmittal (a copy of which is filed as Exhibit (a)(19) hereto),
  the Form of Acceptance, Authority and Election for the Ordinary Shares (a
  copy of which is filed as Exhibit (a)(20) hereto), the Revised Notice of
  Guaranteed Delivery (a copy of which is filed as Exhibit (a)(21) hereto),
  the Form of Proxy for use in connection with the Aran Extraordinary General
  Meeting convened for October 23, 1995 (a copy of which is filed as Exhibit
  (a)(22) hereto), the Advertisement published in the Wall Street Journal on
  October 10, 1995 (a copy of which is filed as Exhibit (a)(23) hereto) and
  the text of the press release dated October 9, 1995 (a copy of which is
  filed as Exhibit (a)(16.9) hereto) is incorporated herein by reference.
 
ITEM 11. MATERIAL TO BE FILED AS EXHIBITS.
 
  Item 11(a) is amended by adding the following exhibits:
 
<TABLE>
      <C>       <S>
      (a)(16.9) Text of press release dated October 9, 1995.
      (a)(17)   Final Cash Offer for Aran Energy plc dated October 9, 1995.
      (a)(18)   Disclosure Document dated October 9, 1995.
      (a)(19)   Revised Letter of Transmittal.
      (a)(20)   Form of Acceptance, Authority and Election for the Ordinary
                Shares.
      (a)(21)   Revised Notice of Guaranteed Delivery.
      (a)(22)   Form of Proxy for use in connection with the Aran Extraordinary
                General Meeting convened for October 23, 1995.
      (a)(23)   Advertisement published in the Wall Street Journal on October
                10, 1995.
</TABLE>
 
                                       2
<PAGE>
 
  After due inquiry and to the best of its knowledge and belief, each of the
undersigned certifies that the information set forth in this statement is
true, complete and correct.
 
Date: October 10, 1995                    Atlantic Richfield Company
 
 
                                          By /s/ Terry G. Dallas
                                          _____________________________________
                                               Vice President & Treasurer
 
                                          ARCO Irish Holdings Inc.
 
 
                                          By /s/ Terry G. Dallas
                                          _____________________________________
                                                  Senior Vice President
 
                                       3
<PAGE>
 
                                 EXHIBIT INDEX
 
<TABLE>
<CAPTION>
 EXHIBIT
 NUMBER                           DESCRIPTION OF DOCUMENT
 -------                          -----------------------
 <C>       <S>
 (a)(16.9) Text of press release dated October 9, 1995.

 (a)(17)   Final Cash Offer for Aran Energy plc dated October 9, 1995.

 (a)(18)   Disclosure Document dated October 9, 1995.

 (a)(19)   Revised Letter of Transmittal.

 (a)(20)   Form of Acceptance, Authority and Election for the Ordinary Shares.

 (a)(21)   Revised Notice of Guaranteed Delivery.

 (a)(22)   Form of Proxy for use in connection with the Aran Extraordinary
           General Meeting convened for October 23, 1995.

 (a)(23)   Advertisement published in the Wall Street Journal October 10, 1995.
</TABLE>

<PAGE>
 
 
                                                              EXHIBIT (a)(16.9)
 
                  [LETTERHEAD OF N M ROTHSCHILD & SONS LIMITED]
 
                                 PRESS RELEASE
 
      NOT FOR RELEASE, PUBLICATION OR DISTRIBUTION IN OR INTO AUSTRALIA, 
                                CANADA OR JAPAN
 
Embargoed until 8:00am                                           9 October 1995
 
                 ARCO'S FINAL* CASH OFFER FOR ARAN ENERGY plc
 
 . ARCO announces a Final Offer of IR68p in cash for each Aran share.
 
 . The Final Offer represents a premium of 60%** over the Aran share price
  before the announcement of the original offer.
 
 . In the event that the Statoil/Connemara proposal is approved at the EGM
  convened for 23 October 1995, or at any adjournment thereof, the
  consideration payable under the Final Offer will be IR66p.
 
Commenting on the Final Offer, Bill Wade, Chairman of ARCO Irish Holdings,
said:
 
  "This Final Offer provides full value for all of Aran's assets. It also
  gives shareholders the opportunity of securing a value for Aran shares
  considerably in excess of market prices existing prior to our original
  offer.
 
  Aran has chosen to complicate matters by requiring shareholders to vote on
  the proposed joint venture that Aran has entered into with Statoil in
  relation to the Connemara field. ARCO is opposed to this proposal and
  believes it transfers value from Aran shareholders to Statoil. From ARCO's
  perspective, the loss of sole operational control of the field has a
  further negative impact over and above the transfer of value. ARCO believes
  the Statoil/Connemara proposal, if approved, would represent a diminution
  in Aran shareholder value.
 
ARCO strongly urges Aran shareholders to:
 
  . vote against the resolution to approve the Statoil/Connemara proposal; and
 
  . accept the increased and final offer without delay."
 
                                    - END -
 
 * The Final Offer is final and will not be extended, nor will it be revised
   or increased, except that ARCO Irish Holdings reserves the right to
   increase, extend ot otherwise revise the Final Offer with the consent of
   the Panel or in the event of a competitive situation (including an offer or
   an intention to make an offer being announced by or on behalf of the
   unnamed third party referred to in Aran's announcement of 6 October 1995)
   arising.
 
** If the Statoil/Connemara proposal is approved the consideration payable
   under the Final Offer is IR66p and would represent a 55% premium over the
   Aran share price before the announcement of the original offer.
 
    New Court, St. Swithin's Lane, London EC4P 4DU Telephone 0171-280 5000 
                        Fax 0171-929 1643 Telex 888031
                               Regulated by SFA
<PAGE>
 
<TABLE>
 <C>                                <S>
 PRESS ENQUIRIES:

 ARCO
 Bill Wade                          Telephone: (44) 171 831 3113
 Terry Dallas                       Telephone: (44) 171 831 3113

 N M ROTHSCHILD & SONS LIMITED      Telephone: (44) 171 280 5000
 Nicholas Wrigley
 Tony Allen

 PUBLIC RELATIONS:

 WHPR                               Telephone: (353) 1 496 0244
 Brian Bell

 FINANCIAL DYNAMICS
 Nick Miles                         Telephone: (44) 171 831 3113
 Marc Popiolek                      Telephone: (44) 171 831 3113
</TABLE>
<PAGE>
 
 NOT FOR RELEASE, PUBLICATION OR DISTRIBUTION IN OR INTO AUSTRALIA, CANADA OR
                                     JAPAN
 
Embargoed until 8:00am                                            9 October 1995
 
                           ARCO IRISH HOLDINGS INC.
                            ("ARCO IRISH HOLDINGS")
 
                         A WHOLLY OWNED SUBSIDIARY OF
 
                          ATLANTIC RICHFIELD COMPANY
                                   ("ARCO")
 
                               FINAL* CASH OFFER
                                      FOR
 
                                ARAN ENERGY PLC
                                   ("ARAN")
 
The Board of ARCO Irish Holdings, a wholly owned subsidiary of ARCO, announces
the terms of an increased and final cash offer to be made on its behalf by N M
Rothschild & Sons Limited to acquire the whole of Aran's issued (and to be
issued) share capital (including Aran shares represented by Aran ADSs).
 
The Final Offer values the existing issued share capital of Aran at
approximately: IR(Pounds)178 million (equivalent to Stg(Pounds)182 million) if
the Statoil/Connemara proposal is NOT approved; or IR(Pounds)173 million
(equivalent to Stg(Pounds)177 million) if the Statoil/Connemara proposal is
approved.
 
The brokers to the Final Offer are Riada Corporate Finance Limited and Hoare
Govett Corporate Finance Limited.
 
THE FINAL OFFER
 
The Final Offer, which will be subject to the conditions and further terms
referred to herein, will be made on the following bases:
 
  (a) If the Statoil/Connemara proposal is voted down
 
    FOR EACH ARAN SHARE              IR68p IN CASH
 
 
    FOR EACH ARAN ADS                IR(Pounds)20.40 IN CASH
    (WHICH REPRESENTS 30 ARAN SHARES)
 
Based on an exchange rate of IR(Pounds)1=Stg(Pounds)1.022 (as set out in the
original offer document), the Final Offer on this basis is equivalent to
Stg69.5p per Aran share and Stg(Pounds)20.85 per Aran ADS. Based on an
exchange rate of IR(Pounds)1=$1.5771 (as set out in the original offer
document), the Final Offer on this basis is equivalent to $1.07 per Aran share
and $32.17 per Aran ADS. Appendix 2 sets out the details of such exchange
rates.
 
  (b) If the Statoil/Connemara proposal is approved
 
    FOR EACH ARAN SHARE              IR66p IN CASH
 
 
    FOR EACH ARAN ADS                IR(Pounds)19.80 IN CASH
    (WHICH REPRESENTS 30 ARAN SHARES)
 
* The Final Offer will close at 1.00pm (Dublin and London time), 9.00am (New
  York City time) on 24 October 1995 unless it has by then become or been
  declared unconditional. The Final Offer is final and will not be extended,
  nor will it be revised or increased, except that ARCO Irish Holdings
  reserves the right to increase, extend or otherwise revise the Final Offer
  with the consent of the Panel or in the event of a competitive situation
  (including an offer or an intention to make an offer being announced by or
  on behalf of the unnamed third party referred to in Aran's announcement of 6
  October 1995) arising.
<PAGE>
 
Based on an exchange rate of IR(Pounds)1=Stg(Pounds)1.022 (as set out in the
original offer document), the Final Offer on this basis is equivalent to
Stg67.5p per Aran share and Stg(Pounds)20.24 per Aran ADS. Based on an
exchange rate of IR(Pounds)1=$1.5771 (as set out in the original offer
document), the Final Offer on this basis is equivalent to $1.04 per Aran share
and $31.23 per Aran ADS. Appendix 2 sets out the details of such exchange
rates.
 
ALL REFERENCES IN THIS ANNOUNCEMENT TO THE VALUE OF THE FINAL OFFER AND
COMPARATIVE FIGURES BASED ON THE FINAL OFFER ASSUME, UNLESS OTHERWISE
SPECIFIED, THAT THE STATOIL/CONNEMARA PROPOSAL IS VOTED DOWN AND, ACCORDINGLY,
THAT THE PRICE UNDER THE FINAL OFFER IS IR68p PER ARAN SHARE.
 
On that assumption, and on the bases set out in Appendix 2:
 
  . the Final Offer values the existing issued share capital of Aran
    (including Aran shares represented by Aran ADSs) at approximately
    IR(Pounds)178 million (equivalent to approximately Stg(Pounds)182
    million).
 
  . the Final Offer represents a premium of 60 per cent. over the last dealt
    price in Dublin of IR42.5p per Aran share on 18 August 1995, the last
    business day before the announcement of the original offer.
 
  . the Final Offer represents a premium of 45 per cent. over the Aran four
    year share price high in Dublin before the announcement of the original
    offer of IR47p per share.
 
VALUATION
 
In the weeks since the original offer, debate has centred around the "true"
value of Aran's assets. In reality there are only two areas of any material
difference between ARCO and Aran.
 
The first is Schiehallion where ARCO has a number of concerns with the
assumptions used by SSI in the "independent" valuation. Nevertheless, if ARCO
accepts SSI's assumptions, but eliminates the inappropriate tax loss
allocation and substitutes what ARCO believes the industry would judge to be a
more appropriate discount rate of 12.5%, the value of Schiehallion is
IR(Pounds)55 million (IR21p per share). It is this valuation which ARCO has
included in its Final Offer.
 
The other area in dispute is in relation to exploration assets where Aran's
valuation strains credibility and, not surprisingly, has been largely ignored
by the market. Nevertheless ARCO has attributed a more than generous price for
these high risk and unproven exploration assets.
 
THE STATOIL/CONNEMARA PROPOSAL
 
Aran has chosen to complicate matters by requiring shareholders to vote on the
proposed joint venture that Aran has entered into with Statoil in relation to
the Connemara field. ARCO is opposed to this proposal and believes it
transfers value from Aran shareholders to Statoil. From ARCO's perspective,
the loss of sole operational control of the field has a further negative
impact over and above the transfer of value. ARCO believes the
Statoil/Connemara proposal, if approved, would represent a diminution in Aran
shareholder value.
 
In ARCO's view, Aran's proposed grant of a low cost option to Statoil on
Connemara is an example of why Aran shareholders should accept ARCO's generous
offer.
 
REDUCED PRICE IF THE STATOIL/CONNEMARA PROPOSAL IS APPROVED
 
In response to Aran electing to put the Statoil/Connemara proposal to a
shareholder vote, ARCO has structured its offer to meet the possibility of the
proposal being approved by shareholders. If approved the price under the Final
Offer will be IR66p per share.
 
ARCO strongly urges Aran shareholders to:
 
  . vote against the resolution to approve the Statoil/Connemara proposal; and
 
  . accept the increased and final offer without delay.
<PAGE>
 
MANAGEMENT AND EMPLOYEES
 
The existing employment rights, including pension rights, of the management
and employees of the Aran Group will be fully safeguarded.
 
ARAN SHARE OPTION SCHEME(S)
 
The Final Offer will extend to any Aran securities unconditionally allotted or
issued prior to the date on which the Final Offer becomes or is declared
unconditional (or such later date or dates as ARCO Irish Holdings may decide),
pursuant to the exercise of options granted under the Aran share option
scheme(s). Appropriate proposals will be made by ARCO Irish Holdings in due
course to holders of options under the Aran share option scheme(s).
 
GENERAL
 
By 3.00pm (Dublin and London time), 10.00am (New York City time) on Saturday 7
October 1995, the second closing date of the original offer, valid acceptances
had been received and not validly withdrawn in respect of 2,579,550 Aran
shares, including Aran shares represented by Aran ADSs, representing
approximately 0.99 per cent. of the issued ordinary share capital of Aran.
None of such acceptances have been received from persons acting in concert
with ARCO Irish Holdings.
 
Neither ARCO Irish Holdings nor any person acting in concert with ARCO Irish
Holdings has acquired or agreed to acquire any Aran shares (or rights over
Aran shares) during the original offer period other than those for which valid
acceptances have been received and not validly withdrawn under the original
offer (subject to the conditions of the original offer) nor did any such
person hold any Aran shares (or rights over Aran shares) prior to the
commencement of the original offer period.
 
ARCO Irish Holdings intends to reduce the acceptance level at the earliest
opportunity. Accordingly, subject to ARCO Irish Holdings not being aware of
any circumstances which constitutes or may result in a breach of or failure to
satisfy any of the remaining conditions to the Final Offer (other than
condition (a), the Acceptance Condition and condition (b) relating to the
granting of Irish Mergers Act clearance), ARCO Irish Holdings intends on 19
October 1995 to give three US Business Days' notice to reduce the acceptance
level so that the Acceptance Condition will have been satisfied if ARCO Irish
Holdings and/or its wholly-owned subsidiaries shall have acquired or agreed to
acquire, pursuant to the Final Offer or otherwise, Aran shares (including Aran
shares represented by Aran ADSs) carrying more than 50 per cent. of the voting
rights normally exercisable at general meetings of Aran, including, for this
purpose, any such voting rights attaching (or which on issue will attach) to
any Aran shares (including Aran shares represented by Aran ADSs) which have
been unconditionally allotted or issued before the Acceptance Condition (as
reduced) is satisfied whether pursuant to the exercise of any outstanding
subscription or conversion rights or otherwise.
 
POSTING OF DOCUMENTS TO SHAREHOLDERS
 
Rothschilds, which is acting as financial adviser to ARCO and ARCO Irish
Holdings, will today despatch the formal Final Offer document and Acceptance
Forms to Aran shareholders. Rothschilds will be acting through Rothschild Inc.
for the purpose of making the Final Offer in the United States.
 
                                    - END -
<PAGE>
 
<TABLE>
 <C>                                <S>
 PRESS ENQUIRIES:

 ARCO
 Bill Wade                          Telephone: (44) 171 831 3113
 Terry Dallas                       Telephone: (44) 171 831 3113

 N M ROTHSCHILD & SONS LIMITED      Telephone: (44) 171 280 5000
 Nicholas Wrigley
 Tony Allen

 PUBLIC RELATIONS:

 WHPR                               Telephone: (353) 1 496 0244
 Brian Bell

 FINANCIAL DYNAMICS
 Nick Miles                         Telephone: (44) 171 831 3113
 Marc Popiolek                      Telephone: (44) 171 831 3113
</TABLE>
 
N M Rothschild & Sons Limited, Hoare Govett Corporate Finance Limited, which
are both regulated by The Securities and Futures Authority Limited in the UK,
and Riada Corporate Finance Limited are acting for the ARCO Group in
connection with the Final Offer and no one else and will not be responsible to
anyone other than the ARCO Group for providing the protections afforded to
their respective customers or for providing advice in relation to the Final
Offer.
 
This announcement does not constitute an offer or invitation to purchase any
securities.
<PAGE>
 
                                  APPENDIX 1
 
                         CONDITIONS OF THE FINAL OFFER
 
The Final Offer is, save as set out herein, subject to the conditions of the
original offer set out in Part A of Appendix 1 to the original offer document
which shall be deemed to be incorporated in and form part of this Appendix
provided that references in such Part A to the Offer shall be deemed to be
references to the Final Offer. References in such Part A to 3.00 pm (Dublin
and London time), 10.00 am (New York City time) on 23 September 1995 shall be
deemed to be references to 1.00 pm (Dublin and London time), 9.00 am (New York
City time) on 24 October 1995.
 
The conditions contained in paragraphs (c), (d) and, with respect to the
references therein to the US HSR Act, (k) of Part A of Appendix 1 to the
original offer document have been fulfilled.
 
ARCO Irish Holdings intends to revise the Acceptance Condition at the earliest
opportunity so that the condition will have been satisfied if ARCO Irish
Holdings and/or its wholly-owned subsidiaries shall have acquired or agreed to
acquire, pursuant to the Final Offer or otherwise, Aran shares (including Aran
shares represented by Aran ADSs) carrying more than 50 per cent. or more of
the voting rights normally exercisable at general meetings of Aran, including,
for this purpose, any such voting rights attaching (or which on issue will
attach) to any Aran shares (including Aran shares represented by Aran ADSs)
which have been unconditionally allotted or issued before the Acceptance
Condition (as reduced) is satisfied whether pursuant to the exercise of any
outstanding subscription or conversion rights or otherwise.
 
Accordingly, subject to ARCO Irish Holdings not being aware of any
circumstance which constitutes or may result in a breach of or failure to
satisfy any of the remaining conditions to the Final Offer (other than
condition (a), the Acceptance Condition, and condition (b) relating to the
granting of Irish Mergers Act clearance), ARCO Irish Holdings intends on 19
October 1995 to give three US Business Days' notice to reduce the acceptance
level as described above with effect on and from 24 October 1995.
 
A reference in the conditions to a public announcement by Aran shall mean an
announcement delivered by or on behalf of Aran to the Company Announcements
Office of the Irish Stock Exchange and the London Stock Exchange and publicly
announced shall be construed accordingly.
 
ARCO Irish Holdings reserves the right to waive (where possible), in whole or
in part, all or any of conditions (b) to (n) inclusive which remain
outstanding or unsatisfied. ARCO Irish Holdings shall be under no obligation
to waive or treat as satisfied any of such conditions by a date earlier than
24 October 1995 notwithstanding that the other conditions of the Final Offer
may at such earlier date have been waived or fulfilled and that there are at
such earlier date no circumstances indicating that any such conditions may not
be capable of fulfilment.
 
ARCO Irish Holdings intends, if appropriate, to seek the Panel's approval to
extend the date by which conditions (b) to (n) inclusive must be satisfied or
waived to not later than 14 November 1995 (or such later date as the Panel may
agree). Unless otherwise determined by ARCO Irish Holdings (with the consent
of the Panel), the Final Offer will lapse unless at the latest time and date
at which the Final Offer shall be terminated or expire ("the closing date")
the Acceptance Condition is or remains satisfied by reference to acceptances
and purchases permitted to be counted towards fulfilling the Acceptance
Condition (other than acceptances withdrawn or before the closing date), and
subject to the consent of the Panel, by reference to the issued share capital
of Aran as at the first time and date on which the Acceptance Condition is
satisfied.
 
If ARCO Irish Holdings is required by the Panel to make an offer for Aran
securities under the provisions of Rule 9 of the City Code, ARCO Irish
Holdings may make such alterations to the conditions, including the Acceptance
Condition, as are necessary to comply with the provisions of that Rule.
 
If the Minister for Enterprise and Employment of Ireland makes an order under
Section 9 of the Mergers Act prohibiting the Acquisition or prohibiting the
Acquisition except on conditions specified in such order, the Final
<PAGE>
 
Offer will lapse unless, in the case of an order prohibiting the Acquisition
except on the conditions specified in such order, ARCO Irish Holdings, in its
absolute discretion, shall decide to accept such conditions.
 
If the Final Offer lapses, the Final Offer will cease to be capable of further
acceptance and accepting Aran securityholders and ARCO Irish Holdings will
cease to be bound by Acceptance Forms (including acceptance forms relating to
the original offer) submitted before the time when the Final Offer lapses.
 
                                  APPENDIX 2
 
               BASES OF CALCULATIONS AND SOURCES OF INFORMATION
 
(a) The value of the issued capital of Aran at the Final Offer price is based
    on 261,741,729 Aran shares (including Aran shares represented by Aran
    ADSs) in issue, as disclosed by Aran in its circular dated 3 October 1995.
 
(b) The share price before the original offer and the share price high in
    Dublin of Aran for the four years before the original offer is derived
    from the Irish Stock Exchange Daily Official List.
 
(c) Applicable exchange rates as derived from the Financial Times dated 24
    August 1995 as set out in the original offer document are:
 
  IR(Pounds)1 = Stg(Pounds)1.022
  IR(Pounds)1 = $1.5771
 
                                  DEFINITIONS
 
The definitions used in the original offer document, save as varied herein,
also apply in this announcement together with the following additional
definitions, unless the context requires otherwise:
 
<TABLE>
 <C>                              <S>
 "original offer"                 the offer by Rothschilds on behalf of ARCO
                                  Irish Holdings contained in the offer
                                  document dated 25 August 1995 to acquire the
                                  Aran securities.

 "the Statoil/Connemara proposal" the proposed farm-out of an aggregate 47.5
                                  per cent, interest in the Connemara Lease
                                  Underwriting by Aran Servicing Limited to
                                  Statoil as set out in a conditional agreement
                                  between such parties dated 28 September 1995.
</TABLE>

<PAGE>

                                                                 EXHIBIT (a)(17)
 
ARCO IRISH HOLDINGS [LOGO]
 
                               Final* Cash Offer
                                      for
                                Aran Energy plc
 
 
 
 
 
 * THE FINAL OFFER IS FINAL AND WILL NOT BE EXTENDED, NOR WILL IT BE REVISED
   OR INCREASED EXCEPT THAT ARCO IRISH HOLDINGS RESERVES THE RIGHT TO
   INCREASE, EXTEND OR OTHERWISE REVISE THE FINAL OFFER WITH THE CONSENT OF
   THE PANEL OR IN THE EVENT OF A COMPETITIVE SITUATION (INCLUDING AN OFFER
   OR AN INTENTION TO MAKE AN OFFER BEING ANNOUNCED BY OR ON BEHALF OF THE
   UNNAMED THIRD PARTY REFERRED TO IN ARAN'S ANNOUNCEMENT OF 6 OCTOBER 1995)
   ARISING.
 
<PAGE>
 
Rule 8 Notices
 
Any person who, alone or acting together with any other person(s) pursuant to
any agreement or any understanding (whether formal or informal), owns or
controls, or becomes the owner or controller of, directly or indirectly, one
per cent. or more of Aran shares (including Aran shares represented by Aran
ADSs) is generally required under the provisions of Rule 8 of the City Code to
notify the Irish Stock Exchange and the London Stock Exchange of every dealing
in such securities during the initial period of the Final Offer or until, if
later, the date on which the Final Offer becomes or is declared unconditional
in all respects, by no later than 12 noon on the business day following the
relevant transaction. Dealings by ARCO, ARCO Irish Holdings or "associates"
(within the meaning of the City Code) of ARCO or ARCO Irish Holdings in Aran
shares or Aran ADSs must also be so disclosed during the currency of the Final
Offer.
 
Applicable Disclosure Requirements
 
The Final Offer is made for securities of an Irish company and, while the
Final Offer is subject to Irish, UK and US disclosure requirements, US
investors should be aware that this document has been prepared in accordance
with Irish and UK format and style, which differs from US format and style. In
particular, the Appendices contain information concerning the Final Offer
responsive to US disclosure requirements that may be material and has not been
summarised elsewhere.
 
The information concerning Aran in this document has been extracted from, or
is based upon, publicly available information on file at the Companies
Registration Office in Ireland and the SEC and other publicly available
information. Except for information provided in accordance with paragraph 6 of
Appendix 2, ARCO and ARCO Irish Holdings have not had access to the books and
records of Aran. ARCO and ARCO Irish Holdings were not involved in the
preparation of such information and are not in a position to verify any such
information.
 
Enforcement of US Federal Securities Laws
 
ARCO has been advised by its Irish counsel, A&L Goodbody and its English
counsel, Clifford Chance, that there is doubt as to the enforceability in
Ireland and England, respectively, in original actions or in actions for
enforcement of judgements of US courts, of liabilities predicated upon the US
federal securities laws.
 
Rule 10b-13 Exemption
 
In accordance with normal UK practice, ARCO Irish Holdings or its nominees or
brokers (acting as agents for ARCO Irish Holdings) or a subsidiary of ARCO
(other than ARCO Irish Holdings) or a special purpose company established and
jointly owned by ARCO and Rothschilds may make certain purchases of Aran
securities outside the United States during the period in which the Final
Offer remains open for acceptance pursuant to relief granted by the SEC staff
from Rule 10b-13 under the US Exchange Act. Further details on this relief are
contained in Appendix 2 under the heading "Market price data and principal
purchases".
 
Final Offer in United States
 
The Final Offer is being made in the United States by N M Rothschild & Sons
Limited acting through Rothschild Inc. References in this document to the
Final Offer being made by N M Rothschild & Sons Limited should be read
accordingly.
 
- --------------------------------------------------------------------------------
 NO PERSON HAS BEEN AUTHORISED TO GIVE ANY INFORMATION OR TO MAKE ANY
 REPRESENTATION ON BEHALF OF ARCO OR ARCO IRISH HOLDINGS NOT CONTAINED IN
 THIS DOCUMENT, THE ORIGINAL OFFER DOCUMENT, THE CIRCULAR DATED 14
 SEPTEMBER 1995 SENT BY ARCO IRISH HOLDINGS TO ARAN SECURITYHOLDERS OR THE
 ACCEPTANCE FORMS (INCLUDING THE ACCEPTANCE FORMS IN RELATION TO THE
 ORIGINAL OFFER) AND, IF GIVEN OR MADE, ANY SUCH INFORMATION OR
 REPRESENTATION MUST NOT BE RELIED UPON AS HAVING BEEN AUTHORISED. NEITHER
 THE DELIVERY OF THIS DOCUMENT AND THE OTHER DOCUMENTS REFERRED TO ABOVE
 NOR ANY PURCHASE PURSUANT TO THE FINAL OFFER SHALL, UNDER ANY
 CIRCUMSTANCES, CREATE ANY IMPLICATION THAT THERE HAS BEEN NO CHANGE IN THE
 AFFAIRS OF ARCO OR ARCO IRISH HOLDINGS OR ARAN SINCE THE DATE AS OF WHICH
 INFORMATION IS FURNISHED OR THE DATE OF THIS DOCUMENT.
- --------------------------------------------------------------------------------

<PAGE>
 
OFFER TO PURCHASE DATED 9 OCTOBER 1995
 
THIS DOCUMENT IS IMPORTANT AND REQUIRES YOUR IMMEDIATE ATTENTION. IF YOU ARE
IN DOUBT ABOUT THIS FINAL OFFER YOU SHOULD CONSULT AN INDEPENDENT FINANCIAL
ADVISER WHO, IN THE CASE OF UK SHAREHOLDERS, IS AUTHORISED UNDER THE FINANCIAL
SERVICES ACT 1986.
 
THIS DOCUMENT SHOULD BE READ IN CONJUNCTION WITH THE ORIGINAL OFFER DOCUMENT
AND THE CIRCULAR FROM ARCO IRISH HOLDINGS TO ARAN SECURITYHOLDERS DATED 14
SEPTEMBER 1995, COPIES OF WHICH ARE AVAILABLE FROM N M ROTHSCHILD & SONS
LIMITED AT NEW COURT, ST SWITHIN'S LANE, LONDON EC4P 4DU AND FROM THE US
DEPOSITARY, AS SET OUT ON PAGE 33.
 
IF YOU HAVE SOLD OR OTHERWISE TRANSFERRED ALL YOUR ARAN SHARES OR ARAN ADSs,
PLEASE PASS THIS DOCUMENT, TOGETHER WITH THE ACCOMPANYING ACCEPTANCE FORMS AND
(WHERE PROVIDED) THE REPLY-PAID ENVELOPE, AS SOON AS POSSIBLE TO THE PURCHASER
OR TRANSFEREE, OR TO THE BANK, STOCKBROKER OR OTHER AGENT THROUGH WHOM THE
SALE OR TRANSFER WAS EFFECTED, FOR ONWARD TRANSMISSION TO THE PURCHASER OR
TRANSFEREE. HOWEVER, SUCH DOCUMENTS SHOULD NOT BE FORWARDED OR TRANSMITTED IN
OR INTO AUSTRALIA, CANADA OR JAPAN.
 
N M Rothschild & Sons Limited, which is regulated by The Securities and
Futures Authority Limited in the UK, is acting for ARCO and ARCO Irish
Holdings in connection with the Final Offer and no one else and will not be
responsible to anyone other than ARCO and ARCO Irish Holdings for providing
the protections afforded to customers of N M Rothschild & Sons Limited or for
providing advice in relation to the Final Offer. N M Rothschild & Sons Limited
is acting through Rothschild Inc. for the purposes of making the Final Offer
in the United States.
 
- -------------------------------------------------------------------------------
 
                               Final* Cash Offer
 
                                      by
 
                         N M Rothschild & Sons Limited
 
                                 on behalf of
 
                          ARCO IRISH HOLDINGS [LOGO]
 
                         a wholly owned subsidiary of
 
                                     ARCO
 
                    to acquire the entire share capital of
 
                                Aran Energy plc
 
                  (including all American Depositary Shares)
 
- -------------------------------------------------------------------------------
 
*THE FINAL OFFER IS FINAL AND WILL NOT BE EXTENDED, NOR WILL IT BE REVISED OR
INCREASED EXCEPT THAT ARCO IRISH HOLDINGS RESERVES THE RIGHT TO INCREASE,
EXTEND OR OTHERWISE REVISE THE FINAL OFFER WITH THE CONSENT OF THE PANEL OR IN
THE EVENT OF A COMPETITIVE SITUATION (INCLUDING AN OFFER OR AN INTENTION TO
MAKE AN OFFER BEING ANNOUNCED BY OR ON BEHALF OF THE UNNAMED THIRD PARTY
REFERRED TO IN ARAN'S ANNOUNCEMENT OF 6 OCTOBER 1995) ARISING.
 
The Final Offer is open for acceptance until 1.00 p.m. (Dublin and London
time), 9.00 a.m. (New York City time), on 24 October 1995 (the "initial
period") unless extended (in accordance with the terms thereof). At the
conclusion of the initial period or on or before the conclusion of any
extension thereof and on the satisfaction or, where permitted, waiver of the
condition(s) to the Final Offer, the purchase of all Aran securities in
respect of which the Final Offer has been validly accepted and not withdrawn
will take place, and the Final Offer will be extended for a subsequent period
of at least fourteen calendar days. Prior to the Final Offer becoming or
otherwise being declared unconditional in all respects, accepting Aran
securityholders will have the right to withdraw their acceptances in respect
thereof. HOWEVER, IN THE EVENT OF THE FINAL OFFER BECOMING OR BEING DECLARED
UNCONDITIONAL IN ALL RESPECTS, NO RIGHTS OF WITHDRAWAL WILL BE AVAILABLE TO
ACCEPTING ARAN SECURITYHOLDERS IN THE SUBSEQUENT PERIOD DURING WHICH THE FINAL
OFFER REMAINS OPEN FOR ACCEPTANCE.
 
The procedure for acceptance is set out on pages 14 to 18 of this document and
in the accompanying Acceptance Forms.
 
ACCEPTANCES SHOULD BE DESPATCHED AS SOON AS POSSIBLE AND IN ANY EVENT SO AS TO
BE RECEIVED NOT LATER THAN 1.00 P.M. (DUBLIN AND LONDON TIME), 9.00 A.M. (NEW
YORK CITY TIME) ON 24 OCTOBER 1995.
 
- -------------------------------------------------------------------------------
 
     N M ROTHSCHILD & SONS LIMITED                      ROTHSCHILD INC.  
           Financial Adviser                           US Dealer Manager 
                                                     
                                                     
<PAGE>
 
Contents
 
<TABLE>
<CAPTION>
                                                                          Page
                                                                          ----
<S>                                                                       <C>
Letter from the Chairman of ARCO Irish Holdings                             4

Letter from Rothschilds                                                    10

 1. Introduction                                                           10
 2. The Final Offer                                                        10
 3. Terms and Conditions of the Final Offer                                11
 4. Financial effects of acceptance of the Final Offer                     12
 5. Management and employees                                               13
 6. Aran share option schemes(s)                                           13
 7. Taxation                                                               13
 8. Procedure for acceptance of the Final Offer by holders of Aran shares  14
 9. Procedure for acceptance of the Final Offer by holders of Aran ADSs    16
10. Substitute acceptance forms                                            18
11. Rights of withdrawal                                                   18
12. Settlement                                                             19
13. Further information                                                    21

Appendices

 1. Conditions and Further Terms of the Final Offer                        22
 2. Additional Information relevant to the Final Offer                     25
 3. Bases of calculations and sources of information                       30

Definitions                                                                32
</TABLE>
 
                                      -2-
<PAGE>
 
                                   IMPORTANT
 
Aran shareholders should note that the price under the Final Offer will be
IR68p per Aran share ONLY IF the Statoil/Connemara proposal is voted down.
Aran shareholders should complete and return the enclosed Form of Proxy voting
AGAINST the resolution.
 
                    --------------------------------------
 
If the Statoil/Connemara proposal is approved the price under the Final Offer
will be reduced to IR66p per Aran share.
 
                    --------------------------------------
 
Cash consideration under the Final Offer
 
<TABLE>
<CAPTION>
                     STATOIL/CONNEMARA     STATOIL/CONNEMARA
                         PROPOSAL              PROPOSAL
                        VOTED DOWN             APPROVED
<S>                  <C>                   <C>
For each Aran share        IR68p                 IR66p
</TABLE>
 
ARCO BELIEVES IT IS CLEARLY IN ARAN SHAREHOLDERS' INTEREST TO VOTE AGAINST THE
STATOIL/CONNEMARA PROPOSAL.
 
                    --------------------------------------
 
All references in this document to the value of the Final Offer and
comparative figures based on the Final Offer assume, unless otherwise
specified, that the Statoil/Connemara proposal is voted down and accordingly
that the price under the Final Offer is IR68p per Aran share.
 
                                      -3-
<PAGE>
 
                          ARCO IRISH HOLDINGS [LOGO]
                            515 South Flower Street
                             Los Angeles, CA 90071
 
                                                                 9 October 1995
 
Dear Sir or Madam,
 
ARCO Irish Holdings today announced an increased and final cash offer for your
Aran shares. Regrettably, the Board of Aran has chosen to complicate matters
by introducing the Statoil/Connemara proposal which ARCO opposes. Your Board's
action has resulted in ARCO offering:--
 
- --If the Statoil/Connemara proposal is voted dow                    IR68pn
 
- --If the Statoil/Connemara proposal is approved                     IR66p
 
Accordingly, upon the successful conclusion of the Final Offer, Aran
shareholders will be entitled to the full IR 68p ONLY IF THEY REJECT THE
STATOIL/CONNEMARA PROPOSAL.
 
Increased and final offer
 
The increased and final offer provides full value for all of Aran's assets. It
also allows you the opportunity of securing a value for your shares
considerably in excess of market prices existing prior to our Original Offer
because it represents:
 
- --a premium over the Aran share price
  before the Original Offer                                          60%*
 
- --a premium over the Aran four year share price high
  before the Original Offer                                          45%*
 
Aran announced on 6 October 1995 that it had received an approach from a third
party which might lead to an offer. The unnamed party requested information on
Aran. By agreeing to that request ARCO believes that Aran has conceded that
its days as an independent company are numbered. REGARDLESS OF THIS
ANNOUNCEMENT ARCO'S OFFER IS THE ONLY OFFER ON THE TABLE.
 
Valuation
 
In the weeks since the Original Offer, debate has centred around the "true"
value of Aran's assets. In reality there are only two areas of any material
difference between ourselves and Aran.
 
The first is Schiehallion, where we have a number of concerns with the
assumptions used by SSI in the "independent" valuation. Nevertheless, if ARCO
accepts SSI's assumptions, but eliminates the inappropriate tax loss
allocation and substitutes what we believe the industry would judge to be a
 
                                      -4-
<PAGE>
 
more appropriate discount rate of 12.5%, the value of Schiehallion is
IR(Pounds)55 million (IR21p per share). It is this valuation which we have
included in our Final Offer.
 
The other area in dispute is in relation to exploration assets where Aran's
valuation strains credibility and, not surprisingly, has been largely ignored
by the market. Nevertheless, and as is illustrated on the next pages, we have
attributed a more than generous price for these high risk and unproven
exploration assets.
 
The Statoil/Connemara proposal
 
Aran has chosen to complicate matters by requiring shareholders to vote on the
proposed joint venture that Aran has entered into with Statoil in relation to
the Connemara field. ARCO is opposed to this proposal and believes it
transfers value from Aran shareholders to Statoil. From ARCO's perspective,
the loss of sole operational control of the field has a further negative
impact over and above the transfer of value. ARCO believes the
Statoil/Connemara proposal, if approved, would represent a diminution in Aran
shareholder value.
 
In ARCO's view, Aran's proposed grant of a low cost option to Statoil on
Connemara is an example of why Aran shareholders should accept ARCO's generous
offer. The background to the Statoil/Connemara proposal and its negative
impact on Aran and its shareholders is addressed in detail on page 8 of this
document.
 
Reduced price, if the Statoil/Connemara proposal is approved
 
In response to Aran electing to put the Statoil/Connemara proposal to a
shareholder vote, ARCO has structured its offer to meet the possibility of the
proposal being approved by shareholders. If approved, the price under the
Final Offer will be IR66p per share.
 
Recommendation
 
We strongly urge you to:
 
- -- vote against the resolution to approve the Statoil/Connemara proposal by
   completing and posting the enclosed Form of Proxy; and
 
- -- accept our increased and final offer without delay.
 
Yours sincerely,
 
/s/ Bill Wade
 
Bill Wade
Chairman
 
 
*The equivalent figures, if the Statoil/Connemara proposal were approved, are
55% and 40%.
 
                                      -5-
<PAGE>
 
                           ARCO's Analysis of Value

 
                                                     ARCO's Values
                                                     ---------------

              Exploration and             )
                Speculative               )
               Developments:              )           IR18p     27%
                                          )           (including premium
                 . Acreage                )           for control)
            . Solan & Strathmore          )            
                . Connemara               )           
                                       
                                       
                                                      
                Schiehallion              )            
                                          )           IR26p     38%
                   Dunlin                 )
                                       
                                       
             Alba & Parliament            ) 
                                          )          IR24p     35%  
           Gryphon & satellites           )           (net of       
                                          )           debt)          
            US proved reserves            )           
                                          )           
            Celtic Sea royalty            )           
                                                      -------   ----
                                                      IR68p     100%
                                                      =======   ===== 
 
          Note: Assuming the Statoil/Connemara proposal is VOTED DOWN.

                                      -6-
<PAGE>
 
<TABLE> 
<CAPTION> 
The Hard Facts                                                   Conclusion
- -------------------------------------------------------------    --------------------
<S>                                                              <C>  
High risk                                                       
 Exploration Acreage                                            
  . West of Shetlands
   -Over (Pounds)1,000,000,000 spent on exploration       
   -Only 2 announced developments                                 Premium price for 
   -Aran's 1995 record in this region -  Drilled 4:               unproven value     
    Disappointments 4
  . West of Ireland - No discovery has ever been 
    declared commercial
 Solan & Strathmore - Recent disappointing appraisal wells
 Connemara - Still undeveloped; economic viability uncertain

 
Medium risk
 Schiehallion
  . Aran's reserves exposed to unitisation and
    therefore could be less
 Dunlin                                                          Generous value for 
  . Mature field, current production                             upside potential    
    below 20% of peak
  . Abandonment and terminal
    uncertainties
 

Low risk
 Large part of value derived from recent
   auction sales                                                 Full value
 
 Full valuation for core producing
 assets allowing for historic UK tax
 losses

</TABLE> 
 
                                      -7-
<PAGE>
 
                  CONNEMARA--DIMINUTION OF SHAREHOLDER VALUE
 
On 28 September 1995 Aran announced the Aran/Statoil Connemara proposal. The
agreement is incomplete because the Joint Operating Agreement is not
finalised. The Statoil/Connemara proposal was made conditional upon relevant
approvals by the Minister of Transport, Energy and Communications, which have
been given. The agreement was also made subject to any conditions the Panel
might impose.
 
Under the Rules of the City Code in relation to "Restrictions on Frustrating
Action", during the currency of an offer, Aran had the choice either to defer
finalising the agreement until such time as the ARCO offer had been concluded
or to seek the approval of Aran shareholders at an Extraordinary General
Meeting ("EGM").
 
The Aran Board elected to seek shareholders' approval and on 3 October 1995
Aran published a notice convening the necessary EGM. By publishing the notice
of meeting on 3 October 1995, Aran could have chosen to convene the meeting as
early as 19 October 1995. Instead, Aran chose to hold the meeting on 23
October 1995, the day before the expiration date of ARCO's Offer,
notwithstanding that Aran could finalise the agreement WITHOUT HOLDING AN EGM
ONCE THE ARCO OFFER HAD BEEN CONCLUDED. ARCO BELIEVES THAT ARAN'S DECISION TO
OPT FOR AN EGM AND TO SELECT A MEETING DATE OF 23 OCTOBER 1995 IS A BLATANT
ATTEMPT TO FRUSTRATE THE DUE PROCESS OF ARCO'S OFFER AND, AS A CONSEQUENCE, TO
COMPLICATE MATTERS FOR ARAN SHAREHOLDERS.
 
ARCO believes that under the terms of the proposed joint venture Aran will be
transferring value away to Statoil:
 
- --  Statoil has in effect been granted an exclusive six months option to
    review Aran's data on Connemara before deciding whether or not to incur
    any material amount of the estimated $18.6 million cost of the work
    programme, including the Extended Well Test.
 
- --  The first 120 days of production from the Extended Well Test will be for
    Statoil's sole account and thereafter, Statoil is entitled to 50% of the
    production. Depending on production rates, ARCO believes Statoil is
    potentially in a position to cover the cost of the entire work
    programme.
 
- --  If the Connemara field extends into any other blocks owned by Aran, Aran
    has agreed to give 47.25 per cent to Statoil for no extra consideration.
 
- --  Aran has given Statoil the right to match any third party offer to
    acquire all or part of Aran's interest outside the Connemara field in
    Blocks 26/28 and 26/29.
 
- --  The agreement provides for Aran and Statoil to be joint operators
    without explanation as to apportionment of duties and liabilities.
 
For these reasons ARCO believes that the Statoil/Connemara proposal is not in
the best interests of Aran shareholders. In addition, from ARCO's perspective,
the loss of sole operational control of Connemara has a further negative
impact over and above the transfer of value.
 
As a result of the Aran Board's decision to put the Statoil/Connemara proposal
to a shareholders' meeting during the currency of ARCO's offer, ARCO has been
compelled to structure the terms of its Final Offer to accommodate the
possibility that the resolution is approved and the value of Aran to ARCO is
thereby reduced.
 
Accordingly, the price under the Final Offer will be IR 68p in cash per share
ONLY IN THE EVENT THAT THE RESOLUTION FAILS. If the resolution is approved,
the price under the Final Offer will be A REDUCED price of IR 66p per share.
 
ARCO URGES ARAN SHAREHOLDERS TO VOTE AGAINST THE RESOLUTION IN ORDER TO HAVE
THE OPPORTUNITY TO RECEIVE THE HIGHER CONSIDERATION FOR THEIR SHARES.
 
                                      -8-
<PAGE>
 
               The benefits of ARCO's Final Offer are compelling
 
- --CAPITAL:
 
<TABLE>
<S>                                                 <C>
  Premium over Aran share price before
  the Original Offer                                60%*

  Premium over Aran 4 year share price high before
  the Original Offer                                45%*
</TABLE>
 
- --SHARE PRICE PERFORMANCE
 
  Aran's shareholders face an uncertain future without ARCO's Final Offer
  and must give careful consideration to what might happen to the value of
  their investment if they do not accept ARCO's Final Offer.
 
     --    Price prior to Original Offer                   IR42.5p
 
     --    Final Offer price                               IR68.0p*
 
     ARAN'S SHARE PRICE IF FINAL OFFER LAPSES?
 
 
                              [ART APPEARS HERE]

CHART DEPICTING THE PRICE MOVEMENT OF THE STOCK IN IR PENCE BEGINNING OCTOBER 
1994 AND CONTINUING THROUGH OCTOBER 1995. IN ADDITION THE GRAPH REFLECTS THE 
PRICE PRIOR TO THE ORIGINAL OFFER (IR42.5p) AND A QUESTION MARK REGARDING THE 
FUTURE PRICE IF THE FINAL OFFER LAPSES.

 
                          Accept the Final Offer Now
 
           * Assuming the Statoil/Connemara proposal is voted down.
 
                                      -9-
<PAGE>
 
                  [LETTERHEAD N M ROTHSCHILD & SONS LIMITED]
 
                                                                 9 October 1995
 
TO ARAN SECURITYHOLDERS AND, FOR INFORMATION ONLY, TO PARTICIPANTS IN THE ARAN
SHARE OPTION SCHEME(S).
 
Dear Sir or Madam,
 
               FINAL CASH OFFER ON BEHALF OF ARCO IRISH HOLDINGS
 
1. INTRODUCTION
 
On 9 October 1995, the Board of ARCO Irish Holdings, a wholly owned subsidiary
of ARCO, announced the terms of an increased and final cash offer, to be made
by Rothschilds on its behalf, for the whole of Aran's issued (and to be
issued) share capital (including Aran shares represented by Aran ADSs). This
letter sets out the formal Final Offer for your Aran securities.
 
The Final Offer values the existing issued share capital of Aran at
approximately: IR(Pounds)178 million (equivalent to Stg(Pounds)182 million) if
the Statoil/Connemara proposal is NOT approved; OR IR(Pounds)173 million
(equivalent to Stg(Pounds)177 million) if the Statoil/Connemara proposal is
approved.
 
THE FINAL OFFER WILL CLOSE AT 1.00 PM (DUBLIN AND LONDON TIME), 9.00 A.M. (NEW
YORK CITY TIME) ON 24 OCTOBER 1995 UNLESS IT HAS BY THEN BECOME OR BEEN
DECLARED UNCONDITIONAL AS TO ACCEPTANCES. IT WILL NOT OTHERWISE BE EXTENDED,
NOR WILL IT BE REVISED OR INCREASED, EXCEPT THAT ARCO IRISH HOLDINGS RESERVES
THE RIGHT TO INCREASE, EXTEND OR OTHERWISE REVISE THE FINAL OFFER WITH THE
CONSENT OF THE PANEL OR IN THE EVENT OF A COMPETITIVE SITUATION (INCLUDING AN
OFFER OR AN INTENTION TO MAKE AN OFFER BEING ANNOUNCED BY OR ON BEHALF OF THE
UNNAMED THIRD PARTY REFERRED TO IN ARAN'S ANNOUNCEMENT OF 6 OCTOBER 1995)
ARISING.
 
2. THE FINAL OFFER
 
On behalf of ARCO Irish Holdings, we hereby offer to acquire, on the terms and
subject to the conditions set out in this document and in the Acceptance
Forms, all Aran shares (including the Aran shares represented by Aran ADSs) on
the following bases:
 
(a) If the Statoil/Connemara proposal is NOT approved
 
<TABLE>
     <S>                                <C>
     FOR EACH ARAN SHARE                IR68P IN CASH
     FOR EACH ARAN ADS                  IR(Pounds)20.40 IN CASH
     (WHICH REPRESENTS 30 ARAN SHARES)
</TABLE>
 
        Registered number 925279 England. Registered office as above. 
                             Regulated by the SFA
 
                                     -10-
<PAGE>
 
Based on an exchange rate of IR(Pounds)1 = Stg(Pounds)1.022, the Final Offer
on this basis is equivalent to Stg69.5p per Aran share and Stg(Pounds)20.85
per Aran ADS. Based on an exchange rate of IR(Pounds)1 = $1.5771, the Final
Offer on this basis is equivalent to $1.07 per Aran share and $32.17 per Aran
ADS. Paragraph (c) of Appendix 3 sets out the details of such exchange rates.
 
(b) If the Statoil/Connemara proposal is approved
 
<TABLE>
      <S>                                <C>
      FOR EACH ARAN SHARE                IR66P IN CASH
      FOR EACH ARAN ADS                  IR(Pounds)19.80 IN CASH
      (WHICH REPRESENTS 30 ARAN SHARES)
</TABLE>
 
Based on an exchange rate of IR(Pounds)1 = Stg(Pounds)1.022, the Final Offer
on this basis is equivalent to Stg67.5p per Aran share and Stg(Pounds)20.24
per Aran ADS. Based on an exchange rate of IR(Pounds)1 = $1.5771, the Final
Offer on this basis is equivalent to $1.04 per Aran share and $31.23 per Aran
ADS. Paragraph (c) of Appendix 3 sets out the details of such exchange rates.
 
Whilst the Final Offer is denominated in Irish pounds, accepting Aran
shareholders and holders of Aran ADSs will instead be entitled to receive
their cash consideration in either pounds sterling or US dollars at prevailing
exchange rates on the latest practicable business day preceding the date of
payment.
 
The Statoil/Connemara proposal will be approved if the resolution to be
proposed at the Extraordinary General Meeting of Aran convened for 23 October
1995 is passed. Accordingly ARAN SHAREHOLDERS WHO WISH TO RECEIVE THE HIGHER
PRICE UNDER THE FINAL OFFER SHOULD VOTE AGAINST THE RESOLUTION AND ARE URGED
TO COMPLETE AND DESPATCH THE ENCLOSED FORM OF PROXY IN ACCORDANCE WITH THE
INSTRUCTIONS ATTACHED TO IT.
 
If the Final Offer becomes or is declared unconditional, it is intended that
an application will be made for the permission granted by the Irish Stock
Exchange and the London Stock Exchange for Aran shares, and by NASDAQ for Aran
ADSs, to be traded on those markets to be revoked. If the Final Offer becomes
or is declared unconditional and if sufficient acceptances are received, ARCO
Irish Holdings intends to apply the provisions of Section 204 of the Irish
Companies Act (set out in Appendix 5 of the Original Offer document) to
acquire compulsorily any outstanding Aran shares (including Aran shares
represented by Aran ADSs) not acquired pursuant to the Final Offer or
otherwise.
 
3. TERMS AND CONDITIONS OF THE FINAL OFFER
 
The Aran shares (including the Aran shares represented by Aran ADSs) will be
acquired by ARCO Irish Holdings fully paid and free from all liens, equitable
interests, charges and encumbrances and together with all rights attaching
thereto on or after 21 August 1995, including voting rights and the right to
receive and retain all dividends and other distributions declared, made or
paid on or after 21 August 1995, whether payable in cash or otherwise.
 
The Final Offer is subject to the relevant conditions and further terms set
out in Appendix 1 of this document and in the Acceptance Forms and to the
provisions relating to acceptance and settlement set out in paragraphs 8, 9
and 12 of this letter.
 
ACCEPTANCES SHOULD BE DESPATCHED AS SOON AS POSSIBLE AND IN ANY EVENT SO AS TO
BE RECEIVED NOT LATER THAN 1.00 P.M. (DUBLIN AND LONDON TIME), 9.00 A.M. (NEW
YORK CITY TIME) ON 24 OCTOBER 1995.
 
The Final Offer is conditional, inter alia, on valid acceptances being
received in respect of not less than 95 per cent. of the Aran shares
(including Aran shares represented by Aran ADSs) to which the Final Offer
relates, or such lesser percentage as ARCO Irish Holdings may decide (the
acceptance level), provided that such condition (the acceptance condition)
shall not be satisfied unless the Minimum Acceptance Condition shall have been
satisfied.
 
 
                                     -11-
<PAGE>
 
ARCO IRISH HOLDINGS INTENDS TO REDUCE THE ACCEPTANCE LEVEL AT THE EARLIEST
OPPORTUNITY. ACCORDINGLY, SUBJECT TO ARCO IRISH HOLDINGS NOT BEING AWARE OF
ANY CIRCUMSTANCE WHICH CONSTITUTES OR MAY RESULT IN A BREACH OF OR FAILURE TO
SATISFY ANY OF THE REMAINING CONDITIONS TO THE FINAL OFFER (OTHER THAN
CONDITION (a), THE ACCEPTANCE CONDITION, AND CONDITION (b) RELATING TO THE
GRANTING OF IRISH MERGERS ACT CLEARANCE), ARCO IRISH HOLDINGS INTENDS ON 19
OCTOBER 1995 TO GIVE THREE US BUSINESS DAYS' NOTICE TO REDUCE THE ACCEPTANCE
LEVEL SO THAT THE ACCEPTANCE CONDITION WILL HAVE BEEN SATISFIED IF ARCO IRISH
HOLDINGS AND/OR ITS WHOLLY-OWNED SUBSIDIARIES SHALL HAVE ACQUIRED OR AGREED TO
ACQUIRE, PURSUANT TO THE FINAL OFFER OR OTHERWISE, ARAN SHARES (INCLUDING ARAN
SHARES REPRESENTED BY ARAN ADSs) CARRYING MORE THAN 50 PER CENT. OF THE VOTING
RIGHTS NORMALLY EXERCISABLE AT GENERAL MEETINGS OF ARAN, INCLUDING, FOR THIS
PURPOSE, ANY SUCH VOTING RIGHTS ATTACHING (OR WHICH ON ISSUE WILL ATTACH) TO
ANY ARAN SHARES (INCLUDING ARAN SHARES REPRESENTED BY ARAN ADSs) WHICH HAVE
BEEN UNCONDITIONALLY ALLOTTED OR ISSUED BEFORE THE ACCEPTANCE CONDITION (AS
REDUCED) IS SATISFIED WHETHER PURSUANT TO THE EXERCISE OF ANY OUTSTANDING
SUBSCRIPTION OR CONVERSION RIGHTS OR OTHERWISE.
 
If, following the proposed reduction in the acceptance level, the Final Offer
is declared unconditional in all respects, withdrawal rights will terminate
immediately, but the Final Offer will remain open for acceptance for a further
period of not less than 14 days.
 
4. FINANCIAL EFFECTS OF ACCEPTANCE OF THE FINAL OFFER
 
(a) Capital
 
The following tables show, for illustrative purposes only and on the bases and
assumptions set out in the notes below, the financial effects of acceptance of
the Final Offer on the capital value for a holder of 100 Aran shares if the
Final Offer becomes or is declared unconditional in all respects:
 
(1) If the Statoil/Connemara proposal is NOT approved
 
<TABLE>
<CAPTION>
                                                                        Stg
                                                   Note  IR(Pounds) (Pounds)(ii)
<S>                                                <C>   <C>        <C>
Cash consideration................................         68.00       69.50
Market value of 100 Aran shares................... (iii)   42.50       43.44
                                                           -----       -----
Increase in capital value.........................         25.50       26.06
                                                           -----       -----
THIS REPRESENTS AN INCREASE OF....................           60%         60%
</TABLE>
 
(2) If the Statoil/Connemara proposal IS approved
 
<TABLE>
<CAPTION>
                                                                        Stg
                                                   Note  IR(Pounds) (Pounds)(ii)
<S>                                                <C>   <C>        <C>
Cash consideration................................         66.00       67.45
Market value of 100 Aran shares................... (iii)   42.50       43.44
                                                           -----       -----
Increase in capital value.........................         23.50       24.01
                                                           -----       -----
THIS REPRESENTS AN INCREASE OF....................           55%         55%
</TABLE>
- ---------
Notes:
(i)   No account has been taken of any potential liability to taxation.
(ii)  The Stg(Pounds) equivalent is based on the exchange rate set out in
      paragraph (c) of Appendix 3.
(iii) The market value shown in the table for Aran shares is based on the last
      dealt price in Dublin of IR42.5p per Aran share on 18 August 1995, being
      the last dealing day before the announcement of the Original Offer, as
      derived from the Irish Stock Exchange Daily Official List.
 
(b) Income
 
In Aran's 1995 interim results, published on 8 September 1995, it was stated
that the Board expects, subject to the satisfactory inclusion of Schiehallion
as an approved field by its banks and in the absence of any unforeseen
circumstances, to recommend the payment of a dividend of IR1p per Aran share
for 1995 when the results for the year are published in March 1996.
 
                                     -12-
<PAGE>
 
However, Aran shareholders have to date never received a dividend. Acceptance
of the Final Offer will provide the opportunity for Aran shareholders to
generate income from their capital for the first time.
 
5. MANAGEMENT AND EMPLOYEES
 
The existing employment rights, including pension rights, of the management
and employees of the Aran Group will be fully safeguarded.
 
6. ARAN SHARE OPTION SCHEME(S)
 
The Final Offer will extend to any Aran securities unconditionally allotted or
issued and fully paid prior to the date on which the Final Offer becomes or is
declared unconditional (or such later date or dates as ARCO Irish Holdings may
decide) pursuant to the exercise of options granted under the Aran share
option scheme(s). Appropriate proposals will be made by ARCO Irish Holdings in
due course to holders of options under the Aran share option scheme(s).
 
7. TAXATION
 
ANY HOLDERS OF ARAN SECURITIES WHO ARE IN ANY DOUBT AS TO THEIR TAX POSITION
SHOULD CONSULT THEIR PROFESSIONAL ADVISER.
 
The following paragraphs are intended as a general guide only and are based on
current legislation and tax authority practice (which may change) and may not
apply to certain categories of Aran securityholders (e.g. dealers in
securities).
 
(a) Irish taxation
 
For holders of Aran securities who are resident or ordinarily resident in
Ireland for tax purposes or who carry on business in Ireland through a branch
or agency to which such Aran securities are attributable, the sale of such
Aran securities pursuant to the Final Offer will constitute a disposal for the
purposes of Irish taxation of capital gains. Such a disposal may, depending on
the individual circumstances of such holders, give rise to a liability to
taxation.
 
A person who is neither resident nor ordinarily resident in Ireland is not
normally subject to Irish capital gains tax on the disposal of Irish assets.
If at the time of any disposal of Aran shares, such shares were not quoted on
a stock exchange and derived their value or the greater part of their value
directly or indirectly from Irish land, buildings or mineral rights, then such
disposal could be subject to Irish capital gains tax notwithstanding that the
person making the disposal is neither resident nor ordinarily resident in
Ireland.
 
(b) UK taxation of capital gains
 
For holders of Aran securities who are resident or ordinarily resident in the
UK for tax purposes or who carry on business in the UK through a branch or
agency to which such Aran securities are attributable and who hold their
shares as an investment, the sale of such Aran securities pursuant to the
Final Offer will constitute a disposal for the purposes of UK taxation of
capital gains. Such a disposal may, depending on the individual circumstances
of such holders, give rise to a liability to taxation.
 
(c) US taxation
 
The summary below addresses certain US federal income tax consequences
applicable to holders of Aran securities who are citizens or residents of the
United States, domestic corporations or otherwise taxed as United States
residents.
 
The receipt of cash pursuant to the Final Offer will be a taxable transaction
for US federal income tax purposes and may also be a taxable transaction under
applicable state, local, foreign and other tax laws.
 
In general, a holder of Aran securities who sells such securities pursuant to
the Final Offer will, for US federal income tax purposes, recognise a gain or
loss equal to the difference between such holders adjusted tax basis in the
Aran securities transferred and the amount of
 
                                     -13-
<PAGE>
 
cash received in exchange therefor. Such gain or loss will generally be
capital gain or loss and will be long-term capital gain or loss if, on the
date of sale, the Aran securities were held for more than one year. A holder
of Aran securities who sells such securities pursuant to the Final Offer may
have a foreign currency exchange gain or loss for US federal income tax
purposes which would be treated as ordinary income or loss. Any such exchange
gain or loss would be in addition to the gain or loss recognised by the holder
on the disposition of Aran securities pursuant to the Final Offer.
 
Further information on the application of US taxation is contained in
paragraph 12 of Appendix 4 of the Original Offer document.
 
(d) Other jurisdictions
 
Aran securityholders who are subject to taxation in jurisdictions other than
Ireland, the UK, or the US should consult their professional adviser before
taking action.
 
8. PROCEDURE FOR ACCEPTANCE OF THE FINAL OFFER BY HOLDERS OF ARAN SHARES
 
ANY FORM OF ACCEPTANCE PREVIOUSLY SUBMITTED AND NOT WITHDRAWN SHALL (WHETHER
OR NOT THE STATOIL/CONNEMARA PROPOSAL IS APPROVED) CONSTITUTE AN ACCEPTANCE OF
THE FINAL OFFER (IN RESPECT OF THE NUMBER OF ARAN SHARES INSERTED OR DEEMED TO
BE INSERTED IN BOX 1 OF THAT FORM OF ACCEPTANCE) WITHOUT THE NEED FOR FURTHER
ACTION.
 
OTHERWISE, TO ACCEPT THE FINAL OFFER IN RESPECT OF YOUR ARAN SHARES you should
complete EITHER Box 1 or Box 1A and/or Box 1B, and Box 3, and if appropriate
Boxes 4 and/or 5, 6 or 7 and sign Box 2 of the Form of Acceptance IN THE
PRESENCE OF A WITNESS, who should also sign in accordance with the
instructions printed thereon. ARAN SHAREHOLDERS' ATTENTION IS PARTICULARLY
DRAWN TO THE INSTRUCTIONS REGARDING BOXES 1, 1A AND 1B OF THE FORM OF
ACCEPTANCE. Further details for accepting the Final Offer are set out below.
Details for accepting the Final Offer in respect of Aran ADSs are set out in
paragraph 9 of this letter.
 
Aran securityholders who hold both Aran shares and Aran ADSs should use the
appropriate Acceptance Form in respect of each holding.
 
(a) Return of the Form of Acceptance
 
The completed, signed and witnessed Form of Acceptance, together with your
share certificate(s) and/or other document(s) of title, should be returned by
hand or by post to the Irish Receiving Agent, AIB Bank, Registrars & New Issue
Department, Bankcentre, P.O. Box 954, Ballsbridge, Dublin 4, or the UK
Receiving Agent, The Royal Bank of Scotland plc, Registrars Department, New
Issues Section, P.O. Box 859, Consort House, East Street, Bedminster, Bristol,
BS99 1XZ or, by hand only (during normal business hours only), to The Royal
Bank of Scotland plc, Registrars Department, New Issues Section, 67 Lombard
Street, London EC3P 3DL. IN THE ABSENCE OF ELECTIONS BEING MADE TO RECEIVE
ALTERNATIVE CURRENCIES, THE CURRENCY IN WHICH YOU RECEIVE YOUR CONSIDERATION
WILL DEPEND ON YOUR REGISTERED ADDRESS. DETAILS OF CURRENCY ARRANGEMENTS ARE
SET OUT IN PARAGRAPH 12 OF THIS LETTER.
 
An Aran shareholder may instead submit the Form of Acceptance, together with
his or her share certificate(s) and/or other document(s) of title, to the US
Depositary First Chicago Trust Company of New York, either by hand or
overnight courier to Suite 4680, 14 Wall Street, Eighth Floor, New York, NY
10005 or by post to Suite 4660, P.O. Box 2559, Jersey City, NJ 07303 who will
receive such Form(s) of Acceptance and certificates and/or other documents of
title on behalf of the UK Receiving Agent and the Irish Receiving Agent.
 
Completed documents should be received by either the Irish Receiving Agent,
the UK Receiving Agent or the US Depositary as soon as possible and in any
event so as to be received NOT LATER THAN 1.00 P.M. (DUBLIN AND LONDON TIME),
9.00 A.M. (NEW YORK CITY
 
                                     -14-
<PAGE>
 
TIME) ON 24 OCTOBER 1995. Aran shareholders with an Irish or a UK registered
address will find enclosed a first class reply-paid envelope for this purpose.
No acknowledgement of receipt of documents will be given. The instructions
printed on the Forms of Acceptance shall be deemed to form part of the terms of
the Final Offer.
 
(b) Share certificates not readily available or lost
 
Even if your share certificate(s) and/or other document(s) of title is/are not
readily available or is/are lost, the Form of Acceptance should nevertheless
be completed, signed and returned as stated above so as to be received NOT
LATER THAN 1.00 P.M. (DUBLIN AND LONDON TIME), 9.00 A.M. (NEW YORK CITY TIME)
ON 24 OCTOBER 1995 and the share certificate(s) and/or other document(s) of
title forwarded as soon as possible thereafter.
 
The completed Form of Acceptance, together with any share certificate(s)
and/or other document(s) of title that you may have available, should be
lodged with the Irish Receiving Agent or the UK Receiving Agent or (if
appropriate), the US Depositary, at the relevant address given above,
accompanied by a letter stating that the balance will follow or that you have
lost one or more of your share certificate(s) and/or other document(s) of
title.
 
In the case of loss, you should then write to Aran's registrars, Bank of
Ireland, Registration Department, P.O. Box 4044, Hume House, Ballsbridge,
Dublin 4, Ireland, advising them of the loss and asking for a letter of
indemnity for the lost share certificate(s) which, when completed in
accordance with the instructions given, should be returned to the Irish
Receiving Agent or the UK Receiving Agent or (if appropriate) the US
Depositary at the relevant address given above.
 
(c) Validity of acceptances
 
Even if your Form of Acceptance is received not complete in all respects or is
not accompanied by the relevant share certificates and/or other document(s) of
title or your acceptance of the Final Offer is in some other way defective
ARCO Irish Holdings and Rothschilds reserve the right (subject to the terms of
the Final Offer) to treat any acceptance of the Final Offer as valid. In that
event, the consideration under the Final Offer will not be despatched until
after the Form of Acceptance is complete in all respects and the share
certificate(s) and/or other document(s) of title or indemnities satisfactory
to ARCO Irish Holdings and Rothschilds has/have been received.
 
(d) Overseas Aran shareholders
 
The attention of Aran shareholders not resident in Ireland, the UK or the US
(and any person, including without limitation, any custodian, nominee or
trustee who may have an obligation to forward this document or any Acceptance
Forms outside Ireland, the UK or the US) is drawn to Part B of Appendix 1. In
particular, such documents should not be forwarded or transmitted in or into
Australia, Canada or Japan.
 
(e) Method of delivery
 
The method of delivery of Aran shares and all other required documents is at
the option and risk of the accepting Aran shareholder. If delivery is by mail,
registered mail with return receipt requested, properly insured, is
recommended. In all cases, sufficient time should be allowed to ensure timely
delivery. No acknowledgement of receipt of documents will be given.
 
Further information regarding procedures for acceptance by Aran shareholders
is referred to in Part B of Appendix 1.
 
If you are in any doubt about the procedure for acceptance please telephone
the Irish Receiving Agent on 01 660 0311 (Ext. 12280) or the UK Receiving
Agent on 0117 937 0666, or the US Depositary on (800) 659 6111 (toll free) or
(201) 324 0137.
 
                                     -15-
<PAGE>
 
9. PROCEDURE FOR ACCEPTANCE OF THE FINAL OFFER BY HOLDERS OF ARAN ADSs
 
Holders of Aran ADSs who have already tendered and not withdrawn their Aran
ADSs in accordance with the procedures set out in the Original Offer document
(including completion and delivery of the Letter of Transmittal accompanying
the Original Offer document) need not take any further action in order for
such Aran ADSs to be tendered pursuant to the Final Offer.
 
Tenders pursuant to the Letter of Transmittal accompanying the Original Offer
document shall be deemed to constitute an acceptance of the Final Offer for
all such Aran ADSs at the applicable price determined as described herein.
However, any holder of Aran ADSs who has previously submitted a Letter of
Transmittal or Notice of Guaranteed Delivery and who wishes to make an
election concerning the Statoil/Connemara proposal, as described below, should
submit the revised Letter of Transmittal accompanying this document.
 
(a) To accept the Final Offer for Aran ADSs
 
For a holder of Aran ADSs validly to accept the Final Offer:
 
(i)  either a properly completed and duly executed Letter of Transmittal (or
     facsimile thereof), together with any required signature guarantees and
     any other required documents, must be received by the US Depositary at
     one of its addresses set out on page 33 of this document, and the Aran
     ADRs evidencing such Aran ADSs must be received by the US Depositary at
     one of such addresses or delivered pursuant to the procedures for book-
     entry transfer referred to in Part B of Appendix 1 (and a confirmation of
     receipt of such transfer received by the US Depositary); or
 
(ii) such holder must comply with the guaranteed delivery procedures referred
     to in Part B of Appendix 1.
 
Delivery of a Letter of Transmittal, the Aran ADRs evidencing tendered Aran
ADSs (or book-entry transfer of such Aran ADSs) and any other required
documents to the US Depositary by a holder of Aran ADSs will be deemed
(without any further action by the US Depositary) to constitute an acceptance
of the Final Offer by such holder in respect of such holder's Aran ADSs,
subject to the terms and conditions set out in this document and the Letter of
Transmittal. The acceptance of the Final Offer by a holder of Aran ADSs
pursuant to the procedures described above, subject to the withdrawal rights
described below, will constitute a binding agreement between such holder of
Aran ADSs and ARCO Irish Holdings upon the terms and subject to the conditions
of the Final Offer. If acceptance has been made in respect of an Aran ADS then
a separate acceptance in respect of the Aran shares represented by such Aran
ADS may not be made.
 
TENDERS OF ARAN ADSs PURSUANT TO THE LETTER OF TRANSMITTAL ACCOMPANYING THE
ORIGINAL OFFER DOCUMENT SHALL BE DEEMED TO CONSTITUTE AN ACCEPTANCE OF THE
FINAL OFFER IN RESPECT OF ALL SUCH ARAN ADSs AT THE APPLICABLE PRICE
DETERMINED AS DESCRIBED HEREIN. THE REVISED LETTER OF TRANSMITTAL PERMITS A
TENDERING HOLDER OF ARAN ADSs TO ELECT, BY COMPLETING THE APPROPRIATE BOX(ES),
EITHER (i) TO ACCEPT THE FINAL OFFER IN RESPECT OF ALL OR SOME OF SUCH
HOLDER'S ARAN ADSs AT THE APPLICABLE PRICE DETERMINED AS DESCRIBED HEREIN,
(ii) TO ACCEPT THE FINAL OFFER ONLY IF THE STATOIL/CONNEMARA PROPOSAL IS NOT
APPROVED BY THE ARAN SHAREHOLDERS (I.E., ONLY AT THE HIGHER PRICE) OR ONLY IF
THE STATOIL/CONNEMARA PROPOSAL IS APPROVED (I.E., ONLY AT THE LOWER PRICE) OR
(iii) TO ACCEPT THE FINAL OFFER IN RELATION TO A DIFFERENT NUMBER OF ARAN ADSs
DEPENDING ON WHETHER THE STATOIL/CONNEMARA PROPOSAL IS OR IS NOT APPROVED BY
THE ARAN SHAREHOLDERS.
 
Delivery of a properly completed and duly executed revised Letter of
Transmittal in accordance with the procedures set forth herein and in the
Original Offer document will automatically constitute a revocation of any
Letter of Transmittal previously delivered by the tendering Aran ADS holder.
 
                                     -16-
<PAGE>
 
COMPLETED LETTERS OF TRANSMITTAL, ARAN ADRs EVIDENCING TENDERED ARAN ADSs (OR
CONFIRMATION OF A BOOK-ENTRY TRANSFER OF SUCH ARAN ADSs) AND ANY OTHER
REQUIRED DOCUMENTS SHOULD BE RECEIVED BY THE US DEPOSITARY AS SOON AS POSSIBLE
AND IN ANY EVENT BY NOT LATER THAN 9.00 A.M. (NEW YORK CITY TIME), 1.00 P.M.
(DUBLIN AND LONDON TIME) ON 24 OCTOBER 1995. NO ACKNOWLEDGEMENT OF RECEIPT OF
DOCUMENTS WILL BE GIVEN. THE INSTRUCTIONS PRINTED ON THE LETTER OF TRANSMITTAL
SHALL BE DEEMED TO FORM PART OF THE TERMS OF THE FINAL OFFER.
 
(b) Partial acceptances
 
If the Final Offer is to be accepted in respect of less than all of the Aran
ADSs evidenced by any Aran ADRs delivered to the US Depositary, then the
holder thereof should so indicate in the Letter of Transmittal by filling in
the number of Aran ADSs in respect of which the Final Offer is being accepted
in the applicable section entitled "Description of Accepting Aran ADSs". In
such case, in the event of the Final Offer becoming unconditional, a new Aran
ADR for the remainder of the Aran ADSs (in respect of which the Final Offer
was not accepted) represented by the old Aran ADR will be sent to the
person(s) signing such Letter of Transmittal (or delivered as such person
properly indicates thereon) as promptly as practicable following the date on
which the Aran ADSs in respect of which the Final Offer had been accepted are
purchased.
 
(c) Guaranteed delivery
 
If a holder of Aran ADSs wishes to accept the Final Offer and the Aran ADRs
evidencing such Aran ADSs are not immediately available or the procedures for
book-entry transfer cannot be completed on a timely basis, or if time will not
permit all required documents to reach the US Depositary prior to the expiry
of the Final Offer such holder's acceptance of the Final Offer may
nevertheless be effected using the guaranteed delivery procedures referred to
in Part B of Appendix 1. Holders of Aran ADSs who deliver a Notice of
Guaranteed Delivery to accept the Final Offer must, inter alia, effect the
deliveries described in paragraph 9(a)(i) of this letter within three trading
days after the date of execution of such Notice of Guaranteed Delivery. For
these purposes, a "trading day" is any day on which NASDAQ is open for
business.
 
HOLDERS OF ARAN ADSs WHO WISH TO ACCEPT THE FINAL OFFER MAY USE EITHER THE
REVISED NOTICE OF GUARANTEED DELIVERY ACCOMPANYING THIS DOCUMENT OR THE NOTICE
OF GUARANTEED DELIVERY ACCOMPANYING THE ORIGINAL OFFER DOCUMENT.
 
COMPLETED NOTICES OF GUARANTEED DELIVERY SHOULD BE RECEIVED BY THE US
DEPOSITARY AS SOON AS POSSIBLE AND IN ANY EVENT BY NOT LATER THAN 9.00 A.M.
(NEW YORK CITY TIME), 1.00 P.M. (DUBLIN AND LONDON TIME) ON 24 OCTOBER 1995.
NO ACKNOWLEDGEMENT OF RECEIPT OF DOCUMENTS WILL BE GIVEN. THE INSTRUCTIONS
PRINTED ON THE NOTICE OF GUARANTEED DELIVERY SHALL BE DEEMED TO FORM PART OF
THE TERMS OF THE FINAL OFFER.
 
HOWEVER, RECEIPT OF A NOTICE OF GUARANTEED DELIVERY WILL NOT BE TREATED AS A
VALID ACCEPTANCE FOR THE PURPOSE OF SATISFYING THE ACCEPTANCE CONDITION. FOR
SUCH ARAN SECURITYHOLDER'S ACCEPTANCE TO BE COUNTED TOWARDS SATISFACTION OF
THE ACCEPTANCE CONDITION, THE US DEPOSITARY MUST HAVE RECEIVED, BY NOT LATER
THAN 9.00 A.M. (NEW YORK CITY TIME), 1.00 P.M. (DUBLIN AND LONDON TIME) ON 24
OCTOBER 1995:
 
(i)  the Aran ADRs evidencing the Aran ADSs referred to in the Notice of
     Guaranteed Delivery; or
 
(ii) in the case of Aran ADSs held in book-entry form, timely confirmation of
     a book-entry transfer of such Aran ADSs into the US Depositary's account
     at a Book-Entry Transfer Facility pursuant to the procedures referred to
     in Part B of Appendix 1,
 
and, in either case, together with a properly completed and duly executed
Letter of Transmittal (or facsimile thereof) with any required signature
guarantees and any other required documents.
 
                                     -17-
<PAGE>
 
Holders of Aran ADSs who deliver a Notice of Guaranteed Delivery to accept the
Final Offer must deliver a Letter of Transmittal at a later date when
delivering Aran ADSs to the US Depositary, as provided herein. Aran
securityholders who hold both Aran shares and Aran ADSs should use the
appropriate Acceptance Form in respect of each holding.
 
(d) Validity of acceptances
 
Even if your Letter of Transmittal or Notice of Guaranteed Delivery, together
with any signature guarantees, are received not complete in all respects or
(unless book-entry transfer of Aran ADSs has been made) your Letter of
Transmittal is not accompanied by the Aran ADRs evidencing tendered Aran ADSs
and/or other documents(s) of title, or your acceptance of the Final Offer is
in some other way defective, ARCO Irish Holdings and Rothschilds reserve the
right (subject to the terms of the Final Offer) to treat any acceptance of the
Final Offer as valid. In that event, the consideration under the Final Offer
will not be despatched until after the Letter of Transmittal, together with
any required signature guarantees, are complete in all respects, and such Aran
ADRs and/or other document(s) of title or indemnities satisfactory to ARCO
Irish Holdings and Rothschilds has/have been received.
 
(e) Overseas Aran ADS holders
 
The attention of holders of Aran ADSs not resident in Ireland, the UK or the
US (and any person, including without limitation, any custodian, nominee or
trustee who may have an obligation to forward this document or any Acceptance
Form(s) outside Ireland, the UK or the US) is drawn to Part B of Appendix 1.
In particular, such documents should not be forwarded or transmitted in or
into Australia, Canada or Japan.
 
(f) Method of delivery
 
The method of delivery of Aran ADSs and all other required documents is at the
option and risk of the accepting Aran ADS holder. If delivery is by mail,
registered mail with return receipt requested, properly insured, is
recommended. In all cases, sufficient time should be allowed to ensure timely
delivery. No acknowledgement of receipt of documents will be given.
 
Further information regarding procedures for acceptance by holders of Aran
ADSs is referred to in Part B of Appendix 1.
 
If you are in any doubt about the procedure for acceptance by holders of Aran
ADSs please telephone the US Depositary on (800) 659 6111 (toll free) or (201)
324 0137.
 
10. SUBSTITUTE ACCEPTANCE FORMS
 
Aran shareholders should use the Form of Acceptance enclosed with this
document to accept the Final Offer in respect of their Aran shares in
accordance with the terms of paragraph 8 above.
 
Holders of Aran ADSs may use either the revised Letter of Transmittal and
Notice of Guaranteed Delivery accompanying this document or the Letter of
Transmittal and Notice of Guaranteed Delivery accompanying the Original Offer
document to accept the Final Offer in respect of their Aran ADSs in accordance
with the terms of paragraph 9 above.
 
Should any Aran securityholder receive an incorrect Acceptance Form with which
to accept the Final Offer, or need any additional Acceptance Forms, he or she
should contact the Irish Receiving Agent, the UK Receiving Agent or the US
Depositary (at the relevant address and telephone number set out on page 33 of
this document), who will provide the appropriate Acceptance Forms.
 
11. RIGHTS OF WITHDRAWAL
 
With certain exceptions pursuant to an SEC exemptive order, the Final Offer is
subject to the US tender offer rules applicable to securities registered under
the US Exchange Act as well as to the rules of the City Code. This has
necessitated a number of changes from the procedures
 
                                     -18-
<PAGE>
 
which normally apply to offers for Irish companies, including those applicable
to offeree shareholders' rights to withdraw their acceptance of an offer.
 
Under the Final Offer, holders of Aran securities will be able to withdraw
their acceptances at any time prior to the Final Offer becoming or being
declared unconditional in all respects. Withdrawals of acceptances in respect
of the Final Offer may not be rescinded without the consent of ARCO Irish
Holdings or Rothschilds and the Final Offer will be deemed not to have been
validly accepted in respect of any Aran securities which have been so
withdrawn. However, the Final Offer may be accepted again in respect of the
withdrawn Aran securities by following one of the procedures described above
in paragraph 8 (Procedure for acceptance of the Final Offer by holders of Aran
shares) or paragraph 9 (Procedure for acceptance of the Final Offer by holders
of Aran ADSs), as appropriate, at any time prior to the expiry or lapse of the
Final Offer.
 
All questions as to the validity (including time of receipt) of notices of
withdrawal will be determined by ARCO Irish Holdings, whose determination
(except as required by the Panel) will be final and binding. None of ARCO
Irish Holdings, Rothschilds, the Irish Receiving Agent, the UK Receiving
Agent, the US Depositary, the US Dealer Manager, or any other person will be
under any duty to give notification of any defects or irregularities in any
notice of withdrawal or incur any liability for failure to give any such
notification.
 
Further details of these rights of withdrawal and the procedure for effecting
withdrawals are referred to in Part B of Appendix 1.
 
12. SETTLEMENT
 
(a) Date of payment
 
The settlement procedure with respect to the Final Offer will be consistent
with Irish and UK practice, which differs from the US tender offer rules in
certain material respects, particularly with regard to the date of payment.
 
Subject to the Final Offer becoming or being declared unconditional in all
respects, cheques drawn on a branch of the Royal Bank of Scotland plc will be
sent by first class post to accepting Aran shareholders, and cheques drawn on
First Chicago Trust Company of New York will be sent by post to accepting
holders of Aran ADSs or other designated agents, in each case at the risk of
the persons entitled thereto:
 
(i)  in the case of acceptances received complete in all respects by the date
     when the Final Offer becomes or is declared unconditional in all
     respects, within 21 days of such date; or
 
(ii) in the case of acceptances received complete in all respects after such
     date but while the Final Offer remains open for acceptance, within 21
     days of such receipt.
 
(b) Currency of consideration
 
Whilst the Final Offer price per Aran share is denominated in Irish pounds,
Aran shareholders with registered addresses in the UK will (subject to
paragraph 12(c) below) receive the cash consideration due to them in pounds
sterling.
 
Whilst the Final Offer price per Aran ADS is denominated in Irish Pounds,
holders of Aran ADSs will (subject to paragraph 12(c) below) receive the cash
consideration due to them in US dollars.
 
All other accepting Aran shareholders will (subject to paragraph 12(c) below)
receive the cash consideration due to them in Irish pounds.
 
(c) Alternative currency election
 
Accepting Aran securityholders may elect, instead of receiving the currency
set out in paragraph 12(b) above, to receive all (but not part) of the cash
consideration due to them in one of the other two currencies referred to in
paragraph 12(b) above:
 
                                     -19-
<PAGE>
 
   (i) Irish pounds payment election
 
   Accepting Aran shareholders with registered addresses in the UK and
   accepting holders of Aran ADSs who wish to receive their cash
   consideration in Irish pounds should put a "X" in the Box of the relevant
   Acceptance Form entitled Irish Pounds Payment Election.
 
   (ii) Pounds sterling payment election
 
   Accepting Aran shareholders with registered addresses outside the UK and
   accepting holders of Aran ADSs who wish to receive their cash
   consideration in pounds sterling should put a "X" in the Box of the
   relevant Acceptance Form entitled Pounds Sterling Payment Election.
 
   The amount of pounds sterling received will be at the noon buying rate
   prevailing in London for transfers in Irish pounds on the latest
   practicable business day preceding the date of despatch of payment as
   certified by The Royal Bank of Scotland plc. All costs of conversion will
   be paid by ARCO Irish Holdings.
 
   The actual amount of pounds sterling received will depend upon the
   exchange rate prevailing on the latest practicable business day preceding
   the date of despatch of payment, which may differ from the exchange rate
   set forth in paragraph 2 above. Aran securityholders should also be aware
   that the exchange rate which is prevailing at the date on which an
   election is made to receive pounds sterling and/or on the date of
   despatch of payment may be different from that prevailing on the latest
   practicable business day preceding the date of despatch of payment. IN
   ALL CASES, FLUCTUATIONS IN THE IRISH POUNDS/POUNDS STERLING EXCHANGE RATE
   ARE AT THE RISK OF ACCEPTING ARAN SECURITYHOLDERS WHO WILL, OR WHO ELECT
   TO, RECEIVE THEIR CONSIDERATION IN POUNDS STERLING.
 
   (iii) US dollars election
 
   Accepting Aran shareholders who wish to receive their cash consideration
   in US dollars should put a "X" in the Box of their Form of Acceptance
   entitled US Dollars Payment Election.
 
   The amount of US dollars received will be at the noon buying rate
   prevailing in London for transfers in Irish pounds on the latest
   practicable business day preceding the date of despatch of payment as
   certified by The Royal Bank of Scotland plc. All costs of conversion will
   be paid by ARCO Irish Holdings.
 
   The actual amount of US dollars received will depend upon the exchange
   rate prevailing on the latest practicable business day preceding the date
   of despatch of payment, which may differ from the exchange rate set forth
   in paragraph 2 above. Aran securityholders should also be aware that the
   exchange rate which is prevailing at the date on which an election is
   made to receive US dollars and/or on the date of despatch of payment may
   be different from that prevailing on the latest practicable business day
   immediately preceding the date of despatch of payment. IN ALL CASES,
   FLUCTUATIONS IN THE IRISH POUNDS/US DOLLAR EXCHANGE RATE ARE AT THE RISK
   OF ACCEPTING ARAN SHAREHOLDERS WHO WILL, OR WHO ELECT TO, RECEIVE THEIR
   CONSIDERATION IN US DOLLARS.
 
(d) General
 
All documents and remittances sent by or to Aran securityholders will be sent
at their own risk. If the Final Offer does not become or is not declared
unconditional in all respects, share certificate(s), Aran ADRs and/or other
document(s) of title, together with the Acceptance Forms, will be returned by
post (or such other method as may be approved by the Panel) within 14 days of
the Final Offer lapsing to the person or agent whose name and address is set
out in the relevant Box of the Acceptance Form (which must be outside
Australia, Canada and Japan)
 
                                     -20-
<PAGE>
 
or, if none is set out, to the first-named holder at his/her registered
address outside Australia, Canada and Japan, or in the case of Aran ADSs
delivered pursuant to the book-entry transfer procedures, as referred to in
Appendix 1.
 
No such documents nor any remittances under the Final Offer will be sent to an
address in Australia, Canada or Japan.
 
13. FURTHER INFORMATION
 
This document should be read in conjunction with the Original Offer document
which contains further information relating to ARCO, ARCO Irish Holdings and
Aran.
 
Your attention is drawn to the Appendices which form part of this document.
 
                              Yours very truly, 
                             for and on behalf of 
                         N M Rothschild & Sons Limited
 
                               Nicholas Wrigley 
                                   Director
 
                                     -21-
<PAGE>
 
APPENDIX 1
 
Conditions and Further Terms of the Final Offer
 
PART A--CONDITIONS OF THE FINAL OFFER
 
The Final Offer is, save as set out herein, subject to the conditions of the
Original Offer set out in Part A of Appendix 1 to the Original Offer document
which shall be deemed to be incorporated in and form part of this Appendix
provided that references in such Part A to the Offer shall be deemed to be
references to the Final Offer. References in such Part A to 3.00 p.m. (Dublin
and London time), 10.00 a.m. (New York City time) on 23 September 1995 shall
be deemed to be references to 1.00 p.m. (Dublin and London time), 9.00 a.m.
(New York City time) on 24 October 1995.
 
The conditions contained in paragraphs (c), (d) and, with respect to the
references therein to the US HSR Act, (k) of Part A of Appendix 1 to the
Original Offer Document have been fulfilled.
 
ARCO Irish Holdings intends to revise the Acceptance Condition at the earliest
opportunity so that the condition will have been satisfied if ARCO Irish
Holdings and/or its wholly-owned subsidiaries shall have acquired or agreed to
acquire, pursuant to the Final Offer or otherwise, Aran shares (including Aran
shares represented by Aran ADSs) carrying more than 50 per cent. of the voting
rights normally exercisable at general meetings of Aran, including, for this
purpose, any such voting rights attaching (or which on issue will attach) to
any Aran shares (including Aran shares represented by Aran ADSs) which have
been unconditionally allotted or issued before the Acceptance Condition (as
reduced) is satisfied whether pursuant to the exercise of any outstanding
subscription or conversion rights or otherwise.
 
Accordingly, subject to ARCO Irish Holdings not being aware of any
circumstance which constitutes or may result in a breach of or failure to
satisfy any of the remaining conditions to the Final Offer (other than
condition (a), the Acceptance Condition, and condition (b) relating to the
granting of Irish Mergers Act clearance), ARCO Irish Holdings intends on 19
October 1995 to give three US Business Days' notice to reduce the acceptance
level as described above with effect on and from 24 October 1995.
 
A reference in the conditions to a public announcement by Aran shall mean an
announcement delivered by or on behalf of Aran to the Company Announcements
Office of the Irish Stock Exchange and the London Stock Exchange and publicly
announced shall be construed accordingly.
 
ARCO Irish Holdings reserves the right to waive (where possible), in whole or
in part, all or any of conditions (b) to (n) inclusive which remain
outstanding or unsatisfied. ARCO Irish Holdings shall be under no obligation
to waive or treat as satisfied any of such conditions by a date earlier than
24 October 1995 notwithstanding that the other conditions of the Final Offer
may at such earlier date have been waived or fulfilled and that there are at
such earlier date no circumstances indicating that any such conditions may not
be capable of fulfilment.
 
ARCO Irish Holdings intends, if appropriate, to seek the Panel's approval to
extend the date by which conditions (b) to (n) inclusive must be satisfied or
waived to not later than 14 November 1995 (or such later date as the Panel may
agree). Unless otherwise determined by ARCO Irish Holdings (with the consent
of the Panel), the Final Offer will lapse unless at the latest time and date
at which the Final Offer shall be terminated or expire ("the closing date")
the Acceptance Condition is or remains satisfied by reference to acceptances
and purchases permitted to be counted towards fulfilling the Acceptance
Condition (other than acceptances withdrawn on or before the closing date),
and subject to the consent of the Panel, by reference to the issued share
capital of Aran as at the first time and date on which the Acceptance
Condition is satisfied.
 
If ARCO Irish Holdings is required by the Panel to make an offer for Aran
securities under the provisions of Rule 9 of the City Code, ARCO Irish
Holdings may make such alterations to the conditions, including the Acceptance
Condition, as are necessary to comply with the provisions of that Rule.
 
                                     -22-
<PAGE>
 
If the Minister for Enterprise and Employment of Ireland makes an order under
Section 9 of the Mergers Act prohibiting the Acquisition or prohibiting the
Acquisition except on conditions specified in such order, the Final Offer will
lapse unless, in the case of an order prohibiting the Acquisition except on
conditions specified in such order, ARCO Irish Holdings, in its absolute
discretion, shall decide to accept such conditions.
 
If the Final Offer lapses, the Final Offer will cease to be capable of further
acceptance and accepting Aran securityholders and ARCO Irish Holdings will
cease to be bound by Acceptance Forms (including acceptance forms relating to
the Original Offer) submitted before the time when the Final Offer lapses.
 
PART B--FURTHER TERMS OF THE FINAL OFFER
 
Except when the context requires otherwise, references in this Appendix 1 and
in the Acceptance Forms to the Final Offer shall mean the Final Offer and any
revision, increase or extension thereof.
 
The Final Offer is a revision of the Original Offer and shall be construed
accordingly.
 
The Final Offer will close at 1.00 p.m. (Dublin and London time), 9.00 a.m.
(New York City time) on 24 October 1995 unless it has by then become or been
declared unconditional. It will not be extended, nor will it be revised or
increased except that ARCO Irish Holdings reserves the right to increase,
extend or otherwise revise the Final Offer with the consent of the Panel or in
the event of a competitive situation (including an offer or an intention to
make an offer being announced by or on behalf of the unnamed third party
referred to in Aran's announcement of 6 October 1995) arising. By midnight
(Dublin and London time) in Ireland and the UK and by midnight (New York City
time) in the US on 24 October 1995, ARCO Irish Holdings will (unless otherwise
permitted by the Panel) make an appropriate announcement as to whether the
Final Offer is unconditional or has lapsed.
 
The Final Offer is, save as set out herein and in the Acceptance Forms, made
on and subject to the conditions and further terms of the Original Offer set
out or referred to in this Appendix 1 and in Part B of Appendix 1 to the
Original Offer document which shall be deemed to be incorporated in and form
part of this Appendix provided that the provisions of such Part B to be so
incorporated shall be varied as follows:
 
   (i)   references to the Offer, except where the context otherwise requires,
         shall be deemed to be references to the Final Offer;
 
   (ii)  references to the Acceptance Forms shall be construed as references
         to the Acceptance Forms as defined in this document, unless the
         context otherwise requires; references to the Form of Acceptance,
         the Letter of Transmittal and the Notice of Guaranteed Delivery
         shall be deemed to be to the Form of Acceptance, the Letter of
         Transmittal and the Notice of Guaranteed Delivery as each is defined
         in this document, unless the context otherwise requires;
 
   (iii) the first sentence of paragraph 1(a) of Part B of Appendix 1 to the
         Original Offer document shall be deemed to be deleted;
 
   (iv)  the following paragraph shall be inserted as a new paragraph
         3(g)(ii)(c) in Part B of Appendix 1 to the Original Offer document
         and the original paragraph 3(g)(ii)(c) shall be redesignated
         paragraph 3(g)(ii)(d) accordingly:
 
         "(c) without prejudice to the authority set out in paragraph (b)
              above:
 
             (i) in the case of an Aran shareholder which is a body corporate,
                 the irrevocable appointment by such Aran shareholder of any
                 director of Rothschilds as its representative in accordance
                 with the articles of association of Aran to attend and speak
                 at the general meeting of Aran convened for 23 October 1995
                 and any adjournment thereof and to exercise the votes of such
                 Aran shareholder attaching to the Relevant Shares on its
                 behalf at such meeting, such votes to be cast against the
                 resolution to be proposed at such meeting;
 
                                     -23-
<PAGE>
 
             (ii) in the case of an Aran shareholder which is not a body
                  corporate, the irrevocable appointment by such Aran
                  shareholder of any director of Rothschilds as such Aran
                  shareholder's attorney and/or agent (the "attorney") and an
                  irrevocable authority to the attorney to attend and speak at
                  the general meeting of Aran convened for 23 October 1995 and
                  any adjournment thereof and to exercise the votes of such
                  Aran shareholder attaching to the Relevant Shares at such
                  meeting, such votes to be cast against the resolution to be
                  proposed at such meeting.
 
          For this purpose "Relevant Shares" shall mean either (i) the
          number of shares shown or deemed to be shown in Box 1 in the
          relevant Form of Acceptance or (ii) if applicable, where a number
          has been inserted in BOTH Box 1A and Box 1B, the number of shares
          equal to the lower of those two numbers."
 
   (v)   the reference to 25 August 1995 in paragraph 8(m) of Part B of
         Appendix 1 to the Original Offer Document shall be deemed to be a
         reference to 10 October 1995;
 
   (vi)  the references in such Part B to 3.00 p.m. (Dublin and London time),
         10.00 a.m. (New York City time) on 23 September 1995 shall be deemed
         to be references to 1.00 p.m. (Dublin and London time), 9.00 a.m.
         (New York City time) on 24 October 1995;
 
   (vii) Paragraph 9 of Part B of Appendix 1 to the Original Offer document
         shall be replaced by the following paragraph:
 
     "9. Overseas Holders of Aran Shares and Aran ADSs
 
             (a) The making of the Final Offer to persons not resident in
                 Ireland, the United Kingdom or the US ("overseas holders")
                 may be affected by the laws of the relevant jurisdiction.
                 Such overseas holders should inform themselves about and
                 observe any applicable legal requirements. It is the
                 responsibility of any overseas holder wishing to accept the
                 Final Offer to satisfy himself or herself as to the full
                 observance of the laws of the relevant jurisdiction in
                 connection therewith, including the obtaining of any
                 governmental, exchange control or other consents which may be
                 required or the compliance with other necessary formalities
                 and the payment of any issue, transfer or other taxes due in
                 such jurisdiction and ARCO Irish Holdings shall be entitled
                 to be fully indemnified and held harmless by such overseas
                 holder for any such issue, transfer or other taxes as ARCO
                 Irish Holdings may be required to pay.
 
             (b) The Final Offer is being made to all holders of Aran
                 securities provided that receipt of this document does not
                 constitute the making of the Final Offer to (and purported
                 acceptance in respect of Aran securities will not be accepted
                 from or on behalf of) Aran securityholders in any
                 jurisdiction in the US or elsewhere in which the making of
                 the Final Offer or the acceptance thereof would not be in
                 compliance with the laws of such jurisdiction. ARCO Irish
                 Holdings is not presently aware of any jurisdiction in the US
                 that prohibits the making of the Final Offer.
 
             (c) In those US jurisdictions whose securities laws or blue sky
                 laws require the Final Offer to be made by a licensed broker
                 or dealer, the Final Offer shall be deemed to be made on
                 behalf of ARCO Irish Holdings by Rothschild Inc. or one or
                 more registered brokers or dealers which are licensed under
                 the laws of those jurisdictions.
 
             (d) The provisions of this paragraph 9 supersede any terms of the
                 Final Offer inconsistent herewith."
 
                                     -24-
<PAGE>
 
APPENDIX 2
 
Additional Information Relevant to the Final Offer
 
1. Introduction
 
This document should be read in conjunction with the Original Offer document
and the document from ARCO Irish Holdings to Aran securityholders dated 14
September 1995 (the "ARCO Letter") to which the announcement in paragraph 4
below relates. The definitions in the Original Offer document also apply to
this document, save where the context requires otherwise. Save as disclosed
herein, the directors of ARCO Irish Holdings and the members of the bid
committee of ARCO are not aware of any material changes to the information set
out in the Original Offer document and the ARCO Letter.
 
2. Responsibility for Information in this Document
 
The directors of ARCO Irish Holdings, whose names are set out in paragraph 2
of Appendix 2 to the Original Offer document, and the members of the bid
committee of ARCO, whose names are set out in paragraph 2 of Appendix 4 to the
Original Offer document, accept responsibility for the information contained
in this document, save that the only responsibility accepted by them in
respect of the information contained in this document relating to the Aran
Group which has been compiled from publicly available Aran Group documents has
been to ensure that such information has been correctly compiled and is
correctly and fairly reproduced and presented. Save as aforesaid, to the best
of the knowledge and belief of the directors of ARCO Irish Holdings and the
bid committee of ARCO (who have taken all reasonable care to ensure that such
is the case), the information contained in this document is in accordance with
the facts and does not omit anything likely to affect the import of such
information.
 
3. Market Price Data and Principal Purchases
 
Aran shares are listed and traded on the Irish Stock Exchange and the London
Stock Exchange and Aran ADSs on NASDAQ. The following table sets out, for the
periods indicated (i) the reported closing highest and lowest share prices for
Aran shares on the Irish Stock Exchange as derived from the Irish Stock
Exchange Daily Official List, (ii) the reported closing highest and lowest
middle market quotations for Aran shares on the London Stock Exchange as
derived from the Daily Official List of the London Stock Exchange and (iii)
the high and low ADS prices on NASDAQ as reported by Datastream. For current
price information, Aran securityholders are urged to consult publicly
available sources.
 
<TABLE>
<CAPTION>
                        Irish Stock Exchange     London Stock Exchange                     NASDAQ
                                 Aran shares               Aran shares                 Aran ADSs*
                                  (IR pence)               (Stg pence)                      (US$)
                             High        Low           High        Low           High        Low
<S>                         <C>          <C>           <C>         <C>           <C>         <C>
Calendar 1993
 Third Quarter               40.0       27.0           36.5       24.5            n/a        n/a
 Fourth Quarter              36.0       21.3           33.5       21.5            n/a        n/a

Calendar 1994
 First Quarter               30.5       25.5           29.5       24.5             n/a       n/a
 Second Quarter              35.0       25.0           33.5       24.5             n/a       n/a
 Third Quarter               41.0       30.0           39.5       30.5           17.50     16.25
 Fourth Quarter              44.5       36.8           43.5       36.5           21.13     17.25

Calendar 1995
 First Quarter               47.0       43.0           46.5       42.5           22.88     20.06
 Second Quarter              46.0       36.8           46.0       39.5           22.50     19.38
 Third Quarter               66.0       36.8           68.0       39.5           32.75     18.75

 Fourth Quarter (up 
  to and including 
  6 October)                 70.8       64.0           72.8       65.8           34.25     31.63
</TABLE>
- ---------
* Aran ADSs were quoted on NASDAQ from 20 September 1994.
 
                                     -25-
<PAGE>
 
The following table shows the middle market quotations for Aran shares as
derived from the London Stock Exchange Daily Official List and last dealt
prices as derived from the Irish Stock Exchange Daily Official List and the
Aran ADS price on NASDAQ as reported by Datastream for (i) the first business
day of each month from February to October 1995; (ii) 18 August 1995 (the last
business day prior to the announcement of the Offer); (iii) 23 August 1995
(the latest practicable date prior to the posting of the Original Offer
document); and (iv) 6 October 1995 (the latest practicable date prior to the
posting of this document):
 
<TABLE>
<CAPTION>
                           Irish Stock Exchange     London Stock Exchange        NASDAQ
                                    Aran shares               Aran shares     Aran ADSs
                                     (IR pence)               (Stg pence)         (US$)
<S>                        <C>                      <C>                       <C>
1 February 1995                            43.5                      43.0         20.40
1 March 1995                               47.0                      46.5         22.00
3 April 1995                               46.0                      46.0         22.50
1 May 1995 (2 May in 
  Ireland)                                 44.0                      44.5         21.75
1 June 1995                                41.0                      42.0         20.50
3 July 1995                                36.8                      39.5         19.44
1 August 1995                              41.0                      42.5         20.69
18 August 1995                             42.5                      44.3         20.63
23 August 1995                             65.3                      67.3         32.25
1 September 1995                           65.5                      68.0         31.75
2 October 1995                             64.0                      65.8         31.63
6 October 1995                             70.8                      72.8         34.25
</TABLE>
 
In accordance with normal UK practice, ARCO Irish Holdings or its nominees or
brokers (acting as agents for ARCO Irish Holdings) or a subsidiary of ARCO
(other than ARCO Irish Holdings) or a special purpose company established and
jointly owned by ARCO and Rothschilds, may make certain purchases of Aran
securities during the period in which the Final Offer remains open for
acceptance pursuant to relief granted from the SEC staff from Rule 10b-13
under the US Exchange Act. In accordance with the terms of this relief, among
other things, (i) such purchases may not be effected within the United States,
(ii) information regarding such purchases must be disclosed in the United
States by press release to the extent disclosure is required pursuant to the
City Code, and (iii) ARCO Irish Holdings and Rothschilds and any such other
persons must comply with any applicable rules of UK and Irish organisations.
 
As at 6 October 1995, the latest practicable date prior to the posting of this
document, ARCO Irish Holdings, whether directly or through any of the other
persons referred to above, had not effected any purchases pursuant to this
authority.
 
4. Text of ARCO announcement dated 20 September 1995
 
"ARCO, in its document to Aran shareholders dated 14 September 1995, set out
its analysis of Aran's assets and associated risks. The Panel on Takeovers and
Mergers has requested ARCO to clarify a number of issues in its analysis,
which it is pleased to do.
 
Aran's core producing assets--low risk
 
<TABLE>
 <C>                           <S>
 Alba and its satellite,       The Union Texas acquisition of the Oryx interest
 Parliament, Gryphon and its   in Block 16/26 included Oryx's interest in both
 satellites                    Alba and Parliament. However, Aran has stated
                               that no value for Oryx's interest in Parliament
                               was included in this sale. As a result, the
                               value of Oryx's interest is not comparable with
                               that of Aran's, which brokers estimate at IR0.3p
                               or IR0.75p per Aran share.
 US proved reserves and        The values referred to in ARCO's analysis of
 Celtic Sea royalty            these interests have been derived from a recent
                               Aran SEC filing containing information
                               calculated in accordance with the requirements
                               of SFAS No. 69. This information does not
                               represent Aran's management's estimate of
                               expected future cash flow or value of proved
                               reserves.
</TABLE>
 
 
                                     -26-
<PAGE>
 
<TABLE>
 <C>                           <S>
                               One of the primary objectives of SFAS No. 69 is
                               stated to be to "develop disclosure requirements
                               that are useful and in particular would
                               compensate, in some measure, for recognised
                               deficiencies in the comparability and predictive
                               value of financial statement information of oil
                               and gas enterprises." The source for this
                               statement is set out in paragraph 2 in the
                               Appendix.

                               The full text of the relevant part of Aran's
                               filing is set out in paragraph 3 of the
                               Appendix.
</TABLE>
 
Taking account of these facts, ARCO remains of the opinion that Aran's core
producing assets (net of Aran's debt) do not have a value of more than IR24p.
 
Aran's other assets--medium to high risk
 
<TABLE>
 <C>                           <S>
 Dunlin                        A recent press article incorrectly attributed to
                               ARCO a statement that the likely abandonment
                               cost, said in the article to have become a hot
                               topic since Shell's experience with Brent Spar,
                               of Dunlin was (Pounds)250 million. Wood
                               Mackenzie has estimated an abandonment cost of
                               (Pounds)200 million on the basis of abandonment
                               in 2007 and before taking account of any
                               potential tax benefits estimated at (Pounds)98
                               million.

 Solan and Strathmore          ARCO's document transposed Aran's interests in
                               these fields and should have been shown as 11.3%
                               and 10% respectively.

 West of Shetland acreage      ARCO pointed out that, since 1972, over 110
                               exploration wells have been drilled at a cost of
                               over (Pounds)1 billion with only 2 announced
                               developments. The source for this statement is
                               set out in paragraph 5 in the Appendix.

                               ARCO stated that nearly 30 appraisal wells have
                               been drilled but public and scout data imply
                               that less than 1 in 3 have been successful. The
                               source for this statement is set out in
                               paragraph 6 of the Appendix.
</TABLE>
 
Aran's Board claims that ARCO has attempted, by its analysis, to create a
smokescreen which it describes as misleading and flawed. ARCO comprehensively
rejects this claim. The reality is that ARCO has sought to advance the debate
by drawing shareholders' attention to the key issues which affect value and by
setting out the questions the Aran Board needs to answer.
 
                                   Appendix
 
1. The brokers' estimates of the value of Aran's interests in Parliament are
   derived from:-
 
  (i)  research published by Cazenove & Co (25 July 1995)--(Pounds)2 million,
       SBC Warburg (14 September 1995)--(Pounds)0.8 million, UBS Global
       Research (May 1995)--(Pounds)2 million;
 
  (ii) translating the above pounds sterling amounts into Irish pounds at a
       rate of IR(Pounds)1= Stg (Pounds)1.022 and dividing the resulting
       figure by 261,741,729, being the number of Aran shares (including
       Aran shares represented by Aran ADSs) in issue as disclosed by Aran
       on 11 September 1995.
 
2. The statement regarding one of the primary objects of SFAS No. 69 is taken
   from the Statement of Financial Accounting Standards No. 69 entitled
   "Disclosures about Oil and Gas Producing Activities" dated November 1982.
 
3. The text of the relevant part of Aran's recent 1994 SEC 20-F filing is set
   out below:
 
  "The standardized measure of discounted future cash flows relating to
  proved crude oil and gas reserves is calculated in accordance with the
  requirements of SFAS 69 and uses reserve definitions prescribed by the
  Financial Accounting Standards Board. Estimated future cash flows from
  production are computed by applying year end prices for crude oil and
  natural gas at year end exchange rates to year end quantities of estimated
  net proved reserves. Future price changes are limited to those provided by
  contractual arrangements in existence at the end of the reporting year.
  Future development and production costs are those estimated future
  expenditures necessary to develop and produce year end estimated proved
  reserves based on year end price levels and assuming the continuance of
  year end economic conditions. Future production costs include estimated
  abandonment liabilities. Estimated future taxes are calculated by applying
  appropriate year end statutory tax rates and reflect allowable deductions,
  tax credits and the tax basis of related assets. Discounted future net cash
  flows are calculated using 10% mid-period discount factors.
 
  The information provided below does not represent management's estimate of
  the Company's expected future cash flows or value of proved reserves.
  Estimates of proved reserves quantities are imprecise and change over time
  as new information becomes available and, in particular, probable and
  possible reserves, which may become proved reserves in 1995 or later, are
  excluded from the calculations. Also, assumptions have been required
  regarding the timing of future production and the timing and amount of
  future development and production costs. The calculations assume the
  economic conditions existing at the end of the reporting year will
  continue. Other different, but equally valid, assumptions might lead to
  significantly different final results.
 
  Although calculated in accordance with SFAS 69, the Group therefore
  cautions against the placing of unwarranted reliance on this information in
  view of the highly arbitrary nature of the assumptions on which it is
  based."
 
4. The statement regarding the estimated abandonment costs of Dunlin is taken
   from a report published by Wood Mackenzie in October 1994.
 
                                     -27-
<PAGE>
 
5. The statement regarding the number and cost of exploration wells since 1972
   is taken from the following sentence as extracted from a report published
   by Wood Mackenzie in May 1995:
 
    "Since the first West of Shetlands exploration well in 1972, over 110
    wells have been drilled in the region at a cost of over (Pounds)1
    billion."
 
6. The following summary table sets out ARCO's sources for the statement
   regarding appraisal wells drilled in the West of Shetland.
 
<TABLE>
<CAPTION>
                                                       Compl'n Well
   Well No.                   Field/Discovery Operator Date    Status O/U Source
   <S>                        <C>             <C>      <C>     <C>    <C> <C>
   204/19-6.................. Foinaven North       BP  95 Jul  aband.   U   WM
   204/20-2..................   Schiehallion       BP  94 Nov  aband.   U   AA
   204/20-5..................   Schiehallion       BP  95 Jul   susp.   O  EIS
   204/24a-2.................       Foinaven       BP  92 Oct  aband.   O  EIS
   204/24a-2y................       Foinaven       BP  92 Nov  aband.   U  EIS
   204/24a-2z................       Foinaven       BP  92 Oct  aband.   U  EIS
   204/24a-3.................       Foinaven       BP  94 May  aband.   U   AA
   204/24a-4.................       Foinaven       BP  94 Jul   susp.   O  EIS
   204/24a-5.................       Foinaven       BP  94 Jul  aband.   U   AA
   204/24a-6.................       Foinaven       BP  94 Aug  aband.   U   AA
   204/24a-7.................       Foinaven       BP  94 Aug  aband.   U   AA
   204/25a-2.................   Schiehallion  Amerada  94 Oct  aband.   O  EIS
   204/25a-3.................   Schiehallion  Amerada  95 Mar  aband.   U   AA
   204/30a-3.................     Strathmore  Amerada  95 Jun  aband.   U   MC
   205/26a-5.................          Solan  Amerada  92 Jul  aband.   U   AA
   205/26a-5z................          Solan  Amerada  92 Aug  aband.   U   AA
   205/26a-6.................          Solan  Amerada  95 Apr  aband.   U   MC
   206/07a-2.................          Clair      Elf  91 Oct  aband.   U  EIS
   206/08-3a.................          Clair       BP  78 Dec  aband.   U  EIS
   206/08-4..................          Clair       BP  79 Feb  aband.   U   AA
   206/08-5..................          Clair       BP  80 Jul   susp.   O  EIS
   206/08-6a.................          Clair       BP  80 Sep  aband.   U   AA
   206/08-7z.................          Clair       BP  85 Nov  aband.   U  EIS
   206/08-8..................          Clair       BP  91 Sep  aband.   O  EIS
   206/08-9z.................          Clair       BP  92 Jul   susp.   O  EIS
   206/13a-2.................          Clair    Exxon  92 Aug  aband.   O  EIS
</TABLE>
 
  In the above table:
 
<TABLE>
   <C> <C> <S>
   O   =   Oil well from which hydrocarbons flowed on test at significant
           rates i.e. more than 1000 barrels per day
   U   =   Unsuccessful well including tight well
   AA  =   Arthur Andersen Petroleum Services
   EIS =   EIS Information Services Limited
   MC  =   Mackay Consultants, as quoted in the Oil and Gas Journal on
           21 August 1995.
   WM  =   Wood Mackenzie                                              "
</TABLE>
 
5. Amount and Source of Funds
 
The amount required to pay the cash consideration for the Aran shares
(including Aran shares represented by Aran ADSs and subject to issuance
pursuant to option schemes), together with estimated fees and expenses, is
estimated to be IR(Pounds)181 million if the Statoil/Connemara proposal is
approved and IR(Pounds)186 million if it is not.
 
The Final Offer will be financed out of existing cash resources available to
the ARCO Group. Neither the payment of interest on, nor repayment of, nor
security for, any liability (contingent or otherwise) of the ARCO Group will
depend to any significant extent on the business of the Aran Group.
Rothschilds is satisfied that the necessary resources are available to ARCO
Irish Holdings to enable it to implement the Final Offer in full.
 
6. General
 
(a) As stated in the Original Offer document, on 19 August 1995, ARCO advised
Morgan Grenfell & Co. Limited ("Morgan Grenfell"), in their capacity as
financial advisers to Aran, that it intended to announce the Original Offer on
21 August 1995. Aran met with ARCO on 6 October 1995. At the meeting, Aran
handed to ARCO the text of an announcement being made by Aran: "The directors
of Aran Energy plc announce that they have received an approach from a third
party which may lead to an alternative offer being made for the share
 
                                     -28-
<PAGE>
 
capital of Aran. The potential offeror has requested information on Aran which
to the extent required by the City Code on Takeovers and Mergers will also be
made available to Arco." No further discussion took place at the meeting. Aran
is making available to ARCO the same data it is providing to the unnamed third
party. Except as described above, the information contained in paragraph 4 of
Appendix 4 to the Original Offer document remains accurate as at 6 October
1995, the latest practicable date prior to the printing of this document.
 
(b) By 3:00 p.m. Dublin and London time (10:00 a.m. New York City time) on
Saturday 7 October 1995, the second closing date of the original cash offer
(the "Original Offer") for the whole of the issued and to be issued share
capital of Aran, valid acceptances had been received and not validly withdrawn
in respect of 2,579,550 Aran shares, including Aran shares represented by Aran
ADSs, representing approximately 0.99 per cent. of the issued ordinary share
capital of Aran. None of such acceptances have been received from persons
acting in concert with ARCO Irish Holdings.
 
Neither ARCO Irish Holdings nor any person acting in concert with ARCO Irish
Holdings has acquired or agreed to acquire any Aran shares (or rights over
Aran shares) during the Original Offer period other than those for which valid
acceptances have been received and not validly withdrawn under the Original
Offer (subject to the conditions of the Original Offer) nor did any such
person hold any Aran shares (or rights over Aran shares) prior to the
commencement of the Original Offer period.
 
7. Documents Available for Inspection
 
The documents listed in paragraph 16 of Appendix 4 to the Original Offer
document, including the Schedule 14D-1 filed with the SEC on 25 August 1995
and subsequent amendments thereto, will be available for inspection at the
offices of A&L Goodbody, 1 Earlsfort Centre, Hatch Street, Dublin 2 and at the
offices of Clifford Chance at 200 Aldersgate Street, London EC1A 4JJ, during
normal business hours on any weekday (Saturdays and public holidays excepted)
whilst the Final Offer remains open for acceptance.
 
 
                                     -29-
<PAGE>
 
APPENDIX 3
 
Bases of Calculations and Sources of Information
 
(a) The value of the existing issued share capital of Aran at the Offer price
    is based on 261,741,729 Aran shares (including Aran shares represented by
    Aran ADSs) in issue, as disclosed by Aran on 3 October 1995.
 
(b) The share price in Dublin of Aran before the Original Offer and the share
    price high in Dublin of Aran for the four years before the Original Offer
    is derived from the Irish Stock Exchange Daily Official List.
 
(c) Applicable exchange rates as derived from the Financial Times dated 24
    August 1995 as set out in the Original Offer document are:
 
  IR(Pounds)1 = Stg(Pounds)1.022
 
  IR(Pounds)1 = $1.5771
 
(d) ARCO's value of Schiehallion on page 4 was determined by creating a net
    present value model which incorporated SSI's assumptions as set out in
    Aran's Circular dated 3 October 1995. This model calculated a value for
    Schiehallion of IR(Pounds)66.3 million -- matching SSI's post corporation
    tax value on a standalone basis (as set out on page 10 of the same Aran
    document). By applying a 12.5% discount rate instead of 10% (SSI's
    discount rate) the model yielded a value of IR(Pounds)55 million.
 
    The "elimination of the inappropriate tax loss allocation" statement on page
     4 refers to SSI's allocation of corporation tax losses to Schiehallion.
     ARCO believes the tax losses are general in nature and are not directly
     tied to Schiehallion and therefore should not be included in the
     Schiehallion field value.
 
    The statement that ARCO's valuation of Aran's core producing assets allows
     for historic UK corporation tax losses on page 7 is based on an analysis of
     the Cairn Energy plc purchase of Clyde Petroleum (North Sea) Limited's 10%
     interest in Gryphon and its satellites for Stg(Pounds)36 million in June
     1995. ERC Tigress Limited valued Gryphon and its satellites for a report
     issued to Cairn Energy shareholders in June 1995. In this report the net
     present value of Cairn's 10% interest in these fields was Stg(Pounds)36
     million which included Stg(Pounds)7.3 million attributable to corporation
     tax losses. Grossing up this figure to reflect Aran's 15% interest in
     Gryphon and its satellites gives an approximate value of Stg(Pounds)11
     million for UK corporation tax losses which ARCO included in its valuation
     of Gryphon and its satellites. SSI's valuation of Aran's UK tax reliefs and
     tax synergy was Stg(Pounds)14.9 million, as set out on page 15 of Aran's
     Circular dated 3 October 1995. However, Stg(Pounds)3.5 million of this is
     attributable to tax relief in respect of future exploration expenditure
     which results in Stg(Pounds)11.4 million being attributable to producing
     assets. Therefore, given ARCO has effectively included Stg(Pounds)11
     million for corporation tax losses in its valuation of Gryphon and its
     satellites, no significant additional value for such losses has been
     included in ARCO's valuation of Aran.
 
(e) The statement that the market has largely ignored Aran's valuation of its
    exploration assets on page 5 is based on the fact that Aran's closing mid
    market share price was Stg 65.62p per Aran share on 2 October 1995 and Stg
    66.87p per Aran share on 3 October 1995, so derived from SEAQ
    International.
 
(f) The source of the statement that Solan and Strathmore were recently the
    subject of disappointing appraisal wells on page 7 is set out on page 4 of
    ARCO's circular dated 14 September 1995.
 
(g) The statement that current production at the Dunlin Field is below 20% of
    peak production on page 7/0/ is determined by contrasting Aran's figures
    of 18,900 barrels per day for the first half of 1995 set out on page 17 of
    their Circular dated 8 September 1995 with the
 
                                     -30-
<PAGE>
 
    peak rate achieved figure of 115,400 barrels per day set out in the Dunlin
    report of the Arthur Andersen United Kingdom Field Analysis Upstream
    Petroleum Database dated July 1995.
 
(h) The statement that a large part of the value attributable to low risk
    assets is derived from auction sales on page 7 is based on the public
    information set out in paragraph 14(f) of Appendix 4 of the Offer Document
    dated 25 August 1995 as amplified by paragraph 3(d) of the Appendix to the
    ARCO Circular dated 14 September 1995 and paragraph 4 of Appendix 2 of
    this document.
 
(i) The bullet point statements on page 8 regarding the terms of the
    Statoil/Connemara proposal are derived from the Agreement between Aran
    Servicing Limited and Statoil (UK) Limited in relation to the Connemara
    Field dated 28 September 1995.
 
(j) The source of the estimated cost figure of US$18.6 million for the
    Connemara work programme on page 8 is derived from Aran's circular dated 3
    October 1995.
 
(k) The graph shown on page 9 of this document is derived from the closing
    share prices as reported by Datastream for each day in the last year from
    7 October 1994 to 6 October 1995.
 
                                     -31-
<PAGE>
 
Definitions
 
The definitions used in the Original Offer document, save as varied herein,
also apply in this document and in the Acceptance Forms, together with the
following additional definitions, unless the context requires otherwise:
 
"Acceptance Forms"         the Form of Acceptance and, with respect to Aran
                           ADS holders only, the Letter of Transmittal and the
                           Notice of Guaranteed Delivery, accompanying this
                           document pursuant to the Final Offer;
 
"approved"                 means, in relation to the Statoil/Connemara
                           proposal, the passing by Aran shareholders at the
                           Extraordinary General Meeting convened for 23
                           October 1995 or any adjournment thereof of the
                           resolution set out in the Notice of Meeting dated 3
                           October 1995;
 
"Final Offer"              the increased and final offer by Rothschilds on
                           behalf of ARCO Irish Holdings contained in this
                           document to acquire the Aran securities, such offer
                           being at a price of IR68p for each Aran share or,
                           if the Statoil/Connemara proposal is approved, a
                           price of IR66p for each Aran share, and in each
                           case, 30 times such amount in respect of each Aran
                           ADS;
 
"Form of Acceptance"       the orange Form of Acceptance, Authority and
                           Election relating to the Final Offer accompanying
                           this document for use by holders of Aran shares;
 
"Letter of Transmittal"    the revised Letter of Transmittal relating to the
                           Final Offer accompanying this document for use by
                           holders of Aran ADSs;
 
"Notice of Guaranteed      the revised Notice of Guaranteed Delivery relating 
Delivery"                  to the Final Offer accompanying this document for  
                           use by holders of Aran ADSs;                        
 
"Original Offer document"  the offer document issued by Rothschilds on behalf
                           of ARCO Irish Holdings dated 25 August 1995;
 
"Original Offer"           the offer by Rothschilds on behalf of ARCO Irish
                           Holdings contained in the Original Offer document
                           to acquire the Aran securities;
 
"SSI"                      Scientific Software-Intercomp
 
"Statoil"                  Statoil (U.K.) Limited; and
 
"the Statoil/Connemara     the proposed farm-out of an aggregate 47.5 per     
proposal"                  cent. interest in the Connemara Lease Undertaking  
                           by Aran Servicing Limited to Statoil as set out in 
                           a conditional agreement between such parties dated 
                           28 September 1995.                                  

 
                                     -32-
<PAGE>
 
Acceptances in respect of Aran Shares
 
Duly completed Forms of Acceptance, accompanied by Aran share certificates
and/or other documents of title, should be delivered to the Irish Receiving
Agent or the UK Receiving Agent at one of the addresses set out below or to the
US Depositary at one of the addresses set out below under acceptances in
respect of Aran ADSs.
 
                                   
The Irish Receiving Agent for the       The UK Receiving Agent for the 
         Final Offer is:                       Final Offer is:
 
                                         The Royal Bank of Scotland plc
             AIB Bank                        Registrar's Department 
     Registrars' & New Issue                   New Issues Section 
            Department                          P.O. Box No 859 
            Bankcentre                           Consort House 
           P.O. Box 954                           East Street 
           Ballsbridge                            Bedminster 
            Dublin 4                               Bristol 
                                                   BS99 IXZ

      For Information Call:                   For Information Call:
 
     01 660 0311 (Ext. 12280)                     0117 937 0666
 

Acceptances in respect of Aran ADSs
 
Manually signed facsimile copies of the Letter of Transmittal will be accepted.
The duly completed Letter of Transmittal, Aran ADRs and any other required
documents should be sent or delivered by each holder of Aran ADSs or his
broker, dealer commercial bank, trust company or other nominee to the US
Depositary at one of its addresses set out below.
 
The US Depositary for the Final Offer is:
 
                    First Chicago Trust Company of New York
 
      By Mail:               For Information Call:        By Hand or Overnight
                                                                Courier:
                    
 First Chicago Trust      (800) 659 6111 (TOLL FREE)       First Chicago Trust  
 Company of New York                  or                   Company of New York  
     Suite 4660                 (201) 324 0137                 Suite 4680       
   P.O. Box 2559                                             14 Wall Street     
  Jersey City, NJ 07303                                       Eighth Floor      
                                                           New York, NY 10005
                                                       
 
Any questions or requests for assistance or additional copies of this document,
the Letter of Transmittal and the Notice of Guaranteed Delivery or the Forms of
Acceptance may be directed to the US Depositary, the Irish Receiving Agent or
the UK Receiving Agent at their respective addresses and telephone numbers set
out above. You may also contact your appropriately advised local broker,
dealer, commercial bank or trust company or other nominee for assistance
concerning the Final Offer.
 
The financial adviser to ARCO and          The US Dealer Manager for the
     ARCO Irish Holdings is:                     Final Offer is:
 
  N M Rothschild & Sons Limited                  Rothschild Inc.
            New Court                      1251 Avenue of the Americas
        St. Swithin's Lane                         51st Floor
         London EC4P 4DU                       New York, NY 10020
 
 
                                      -33-
<PAGE>
 
 
                   Printed by RR Donnelley Financial, 16383p

<PAGE>
 
                                                                 EXHIBIT (a)(18)

DISCLOSURE DOCUMENT DATED OCTOBER 9, 1995
 
THIS DISCLOSURE DOCUMENT IS IMPORTANT AND REQUIRES YOUR IMMEDIATE ATTENTION.
IF YOU ARE IN DOUBT ABOUT THE FINAL OFFER YOU SHOULD CONSULT AN INDEPENDENT
FINANCIAL ADVISER.
 
THE FINAL OFFER IS MADE IN THE UNITED STATES SOLELY BY THE FINAL OFFER
DOCUMENT DATED OCTOBER 9, 1995 (TOGETHER WITH THIS DISCLOSURE DOCUMENT), THE
ORIGINAL OFFER DOCUMENT DATED AUGUST 25, 1995 AND THE RELATED ACCEPTANCE FORMS
(WHICH COLLECTIVELY CONSTITUTE THE FINAL OFFER) AND IS NOT BEING MADE TO, NOR
WILL THE FINAL OFFER BE ACCEPTED FROM OR ON BEHALF OF, HOLDERS OF ARAN
ORDINARY SHARES OR ARAN ADSs IN ANY JURISDICTION IN WHICH THE MAKING OR
ACCEPTANCE THEREOF WOULD NOT BE IN COMPLIANCE WITH THE LAWS OF SUCH
JURISDICTIONS. IN THOSE JURISDICTIONS WHOSE SECURITIES LAWS OR BLUE SKY LAWS
REQUIRE THE FINAL OFFER TO BE MADE BY A LICENSED BROKER OR DEALER, THE FINAL
OFFER SHALL BE DEEMED TO BE MADE ON BEHALF OF ARCO IRISH HOLDINGS INC. BY
ROTHSCHILD INC. OR ONE OR MORE REGISTERED BROKERS OR DEALERS WHICH ARE
LICENSED UNDER THE LAWS OF THOSE JURISDICTIONS.
 
IF YOU HAVE SOLD OR OTHERWISE TRANSFERRED YOUR ARAN ORDINARY SHARES OR ARAN
ADSs, PLEASE PASS THE FINAL OFFER DOCUMENT, TOGETHER WITH THIS DISCLOSURE
DOCUMENT AND THE ACCOMPANYING ACCEPTANCE FORMS, AS SOON AS POSSIBLE TO THE
PURCHASER OR TRANSFEREE, OR TO THE BANK, STOCKBROKER OR OTHER AGENT THROUGH
WHOM THE SALE OR TRANSFER WAS EFFECTED, FOR ONWARD TRANSMISSION TO THE
PURCHASER OR TRANSFEREE. HOWEVER, SUCH DOCUMENTS, THE ORIGINAL OFFER DOCUMENT
AND RELATED MATERIALS SHOULD NOT BE FORWARDED OR TRANSMITTED IN OR INTO
AUSTRALIA, CANADA OR JAPAN.
 
- -------------------------------------------------------------------------------
 
                               Final Cash Offer
 
                                      by
 
                         N M Rothschild & Sons Limited
 
                                 on behalf of
 
                          ARCO IRISH HOLDINGS [LOGO]
 
                         a wholly owned subsidiary of
 
                                     ARCO
 
                          to acquire all outstanding
                Ordinary Shares and American Depositary Shares
 
                                      of
 
                                Aran Energy plc
 
- -------------------------------------------------------------------------------
<PAGE>
 
  N M Rothschild & Sons Limited, acting in the United States through
Rothschild Inc., on behalf of ARCO Irish Holdings Inc. ("ARCO Irish
Holdings"), a wholly owned subsidiary of Atlantic Richfield Company ("ARCO"),
is offering to purchase the entire issued (and to be issued) share capital of
Aran Energy plc ("Aran"), upon the terms and subject to the conditions set
forth in the Offer Document dated August 25, 1995 (the "Original Offer
Document"), the Final Offer Document dated October 9, 1995 (together with this
disclosure document, the "Final Offer Document") and the related Acceptance
Forms on the following bases:
 
 . For each Ordinary Share ("Aran Share"): IR68p in cash
 
 . For each American Depositary Share 
  ("Aran ADS") which represents 30 Aran
  Shares:                                 IR(Pounds)20.40 in cash
 
  IN THE EVENT THAT THE STATOIL/CONNEMARA PROPOSAL (BEING THE PROPOSED FARM-
OUT OF AN AGGREGATE 47.5% INTEREST IN THE CONNEMARA LEASE UNDERTAKING BY ARAN
SERVICING LIMITED TO STATOIL (U.K.) LIMITED ("STATOIL")) IS APPROVED AT THE
EXTRAORDINARY GENERAL MEETING OF ARAN SHAREHOLDERS CONVENED FOR OCTOBER 23,
1995 OR AT ANY ADJOURNMENT THEREOF (THE "ARAN MEETING"), THE CONSIDERATION
PAYABLE UNDER THE FINAL OFFER WILL INSTEAD BE AS FOLLOWS:
 
 . For each Aran Share:                    IR66p in cash
 
 . For each Aran ADS which represents 
  30 Aran Shares:                         IR(Pounds)19.80 in cash
 
  ARCO AND ARCO IRISH HOLDINGS ARE OPPOSED TO THE STATOIL/CONNEMARA PROPOSAL
AND BELIEVE IT TRANSFERS VALUE FROM ARAN SHAREHOLDERS TO STATOIL. ACCORDINGLY,
ARCO AND ARCO IRISH HOLDINGS HAVE STRUCTURED THE FINAL OFFER TO MEET THE
POSSIBILITY OF THE STATOIL/CONNEMARA PROPOSAL BEING APPROVED AND THE RESULTING
DIMINUTION IN SHAREHOLDER VALUE.
 
                     KEY POINTS FOR ARAN'S SECURITYHOLDERS
 
 . The Final Offer will be open for acceptance until 1:00 p.m. (Dublin and
   London time), 9:00 a.m. (New York City time), on October 24, 1995. It will
   not be extended, nor will it be revised or increased, except that ARCO
   Irish Holdings reserves the right to increase, extend or otherwise revise
   the Final Offer should the U.K. Panel on Takeovers and Mergers (the "U.K.
   Panel") so agree or in the event of a competitive situation (including an
   offer or an intention to make an offer being announced by or on behalf of
   the unnamed third party referred to in Aran's announcement of October 6,
   1995) arising (as determined by the U.K. Panel).
 
 . The Final Offer is conditioned, among other things, on valid acceptances
   being received in respect of not less than 95% of the Aran Shares
   (including Aran Shares represented by Aran ADSs) to which the Final Offer
   relates, or such lesser percentage as ARCO Irish Holdings may decide (the
   "acceptance level"), provided that such condition (the "Acceptance
   Condition") shall not be satisfied unless ARCO Irish Holdings and/or its
   wholly owned subsidiaries shall have acquired or agreed to acquire,
   pursuant to the Final Offer or otherwise, Aran Shares (including Aran
   Shares represented by Aran ADSs) carrying more than 50% of the voting
   rights normally exercisable at general meetings of Aran. ARCO Irish
   Holdings intends to revise the Acceptance Condition at the earliest
   opportunity so that the condition will have been satisfied if ARCO Irish
   Holdings and/or its wholly owned subsidiaries shall have acquired or
   agreed to acquire, pursuant to the Final Offer or otherwise, Aran Shares
   (including Aran Shares represented by Aran ADSs) carrying more than 50% of
   the voting rights normally exercisable at general meetings of Aran,
   including, for this purpose, any such voting rights attaching (or which on
   issue will attach) to any Aran Shares (including Aran Shares represented
   by Aran ADSs) which have been unconditionally allotted or issued before
   the Acceptance Condition (as reduced) is satisfied whether pursuant to the
   exercise of any outstanding subscription or conversion rights or
   otherwise. Accordingly, subject to ARCO Irish Holdings not being aware of
   any circumstance which constitutes or may result in a breach of or failure
   to satisfy any of the remaining conditions to the Final Offer (other than
   condition (a), the Acceptance Condition, and condition (b) relating to the
   granting of Irish Mergers Act clearance), ARCO Irish Holdings intends on
   October 19, 1995 to give three U.S. Business Days' notice to reduce the
   acceptance level as described above with effect on and from October 24,
   1995.
 
                                       2
<PAGE>
 
 . Holders of Aran Shares who wish to accept the Final Offer should use the
   Revised Form of Acceptance. THE REVISED FORM OF ACCEPTANCE PERMITS A
   TENDERING HOLDER OF ARAN SHARES TO ELECT, BY COMPLETING THE APPROPRIATE
   BOX(ES), EITHER (i) TO ACCEPT THE FINAL OFFER IN RESPECT OF ALL OR SOME OF
   SUCH HOLDER'S ARAN SHARES AT THE APPLICABLE PRICE DETERMINED AS DESCRIBED
   ABOVE, (ii) TO ACCEPT THE FINAL OFFER ONLY IF THE STATOIL/CONNEMARA
   PROPOSAL IS VOTED DOWN BY THE ARAN SHAREHOLDERS AT THE ARAN MEETING (I.E.,
   ONLY AT THE HIGHER PRICE) OR ONLY IF THE STATOIL/CONNEMARA PROPOSAL IS
   APPROVED (I.E., ONLY AT THE LOWER PRICE) OR (iii) TO ACCEPT THE FINAL
   OFFER IN RELATION TO A DIFFERENT NUMBER OF ARAN SHARES DEPENDING ON
   WHETHER THE STATOIL/CONNEMARA PROPOSAL IS OR IS NOT APPROVED BY THE ARAN
   SHAREHOLDERS AT THE ARAN MEETING. COPIES OF THE REVISED FORM OF ACCEPTANCE
   ARE AVAILABLE FROM THE U.S. DEPOSITARY AT THE ADDRESSES AND TELEPHONE
   NUMBERS SET FORTH BELOW.
 
 . Holders of Aran ADSs who wish to accept the Final Offer should use (i)
   either the Revised Letter of Transmittal or the Letter of Transmittal
   accompanying the Original Offer Document and (ii) if such tendering holder
   wishes to utilize the guaranteed delivery procedures set forth in the
   Final Offer, either the Revised Notice of Guaranteed Delivery or the
   Notice of Guaranteed Delivery accompanying the Original Offer Document.
   TENDERS OF ARAN ADSs PURSUANT TO THE LETTER OF TRANSMITTAL ACCOMPANYING
   THE ORIGINAL OFFER DOCUMENT SHALL BE DEEMED TO CONSTITUTE AN ACCEPTANCE OF
   THE FINAL OFFER IN RESPECT OF ALL SUCH ARAN ADSs AT THE APPLICABLE PRICE
   DETERMINED AS DESCRIBED ABOVE. THE REVISED LETTER OF TRANSMITTAL PERMITS A
   TENDERING HOLDER OF ARAN ADSs TO ELECT, BY COMPLETING THE APPROPRIATE
   BOX(ES), EITHER (i) TO ACCEPT THE FINAL OFFER IN RESPECT OF ALL OR SOME OF
   SUCH HOLDER'S ARAN ADSs AT THE APPLICABLE PRICE DETERMINED AS DESCRIBED
   ABOVE, (ii) TO ACCEPT THE FINAL OFFER ONLY IF THE STATOIL/CONNEMARA
   PROPOSAL IS VOTED DOWN BY THE ARAN SHAREHOLDERS AT THE ARAN MEETING (I.E.,
   ONLY AT THE HIGHER PRICE) OR ONLY IF THE STATOIL/CONNEMARA PROPOSAL IS
   APPROVED (I.E., ONLY AT THE LOWER PRICE) OR (iii) TO ACCEPT THE FINAL
   OFFER IN RELATION TO A DIFFERENT NUMBER OF ARAN ADSs DEPENDING ON WHETHER
   THE STATOIL/CONNEMARA PROPOSAL IS OR IS NOT APPROVED BY THE ARAN
   SHAREHOLDERS AT THE ARAN MEETING. COPIES OF THE REVISED LETTER OF
   TRANSMITTAL AND THE REVISED NOTICE OF GUARANTEED DELIVERY ARE AVAILABLE
   FROM THE U.S. DEPOSITARY AT THE ADDRESSES AND TELEPHONE NUMBERS SET FORTH
   BELOW.
 
 . THERE CAN BE NO ASSURANCE THAT THE RESULTS OF THE ARAN MEETING WILL BE
   AVAILABLE PRIOR TO THE TERMINATION OF WITHDRAWAL RIGHTS. ACCORDINGLY, WE
   URGE YOU TO CONSIDER CAREFULLY THE ELECTIONS YOU CAN MAKE REGARDING THE
   STATOIL/CONNEMARA PROPOSAL IN THE REVISED FORM OF ACCEPTANCE AND THE
   REVISED LETTER OF TRANSMITTAL. PLEASE NOTE THAT IF YOU SUBMIT A DULY
   EXECUTED REVISED FORM OF ACCEPTANCE OR REVISED LETTER OF TRANSMITTAL AND
   FAIL TO MAKE ANY ELECTION REGARDING THE BASIS ON WHICH YOU ARE ACCEPTING
   THE FINAL OFFER, YOU WILL BE DEEMED TO HAVE ACCEPTED THE FINAL OFFER IN
   RESPECT OF ALL ARAN SHARES OR ARAN ADSs TENDERED THEREBY AT THE APPLICABLE
   PRICE DETERMINED AS DESCRIBED ABOVE.
 
 . Withdrawals of previous tenders of Aran ADSs pursuant to Letters of
   Transmittal may be made in writing or by facsimile transmission to the
   U.S. Depositary at the addresses and facsimile copy number set forth below
   in accordance with the procedures set forth in the Final Offer Document
   and the Original Offer Document. Aran ADS holders may submit such
   facsimile withdrawals 24 hours a day, up to 9:00 a.m. (New York City time)
   on October 24, 1995. Delivery of a properly completed and duly executed
   Revised Letter of Transmittal in accordance with the procedures set forth
   in the Final Offer Document and the Original Offer Document will
   automatically constitute a revocation of any Letter of Transmittal
   previously delivered by the tendering Aran ADS holder.
 
                                       3
<PAGE>
 
 . Aran securityholders may telephone the U.S. Depositary at (800) 659-6111
   (Toll Free 24 Hours) in order to obtain the results of the Aran Meeting
   (when disclosed by Aran).
 
 . COMPLETION OF THE ACCEPTANCE PROCEDURES WILL TAKE LONGER THAN YOU EXPECT.
   DON'T WAIT FOR THE LAST MOMENT!
 
  This disclosure document should be read in conjunction with the Final Offer
Document and the Original Offer Document, which contain a complete description
of the terms of the Final Offer. Requests for assistance or copies of the
Final Offer Document, the Original Offer Document, the circular from ARCO
Irish Holdings to Aran securityholders dated September 14, 1995, the Revised
Form of Acceptance, the Revised Letter of Transmittal and the Revised Notice
of Guaranteed Delivery may be directed to the U.S. Depositary at the addresses
and telephone numbers set forth below, and copies will be furnished promptly
at ARCO Irish Holdings' expense.
 
                  The U.S. Depositary for the Final Offer is:
 
                    FIRST CHICAGO TRUST COMPANY OF NEW YORK
 
                                  Suite 4680
                                14 Wall Street
                                 Eighth Floor
                           New York, New York 10005
 
        Facsimile Copy Number:                  For Information Call:
        (201) 222-4720 or 4721               (800) 659-6111 (Toll Free)
         Confirm by Telephone:                    or (201) 324-0137
            (201) 422-4707
 
               By Mail:                     By Hand or Overnight Courier:
              Suite 4660                             Suite 4680
             P.O. Box 2559                         14 Wall Street
     Jersey City, New Jersey 07303                  Eighth Floor
                                              New York, New York 10005
 
        The Dealer Manager for the Final Offer in the United States is:
 
                                ROTHSCHILD INC.
 
                          1251 Avenue of the Americas
                                  51st Floor
                              New York, NY 10020
                      (212) 403-3611 within New York City
          (800) 753-5151 ext. 3611 (Toll Free) outside New York City
 
October 9, 1995
 
                                       4

<PAGE>
 
                                                                 EXHIBIT (a)(19)

THIS DOCUMENT IS IMPORTANT AND REQUIRES YOUR IMMEDIATE ATTENTION. If you are
in any doubt about the action you should take, you are recommended to seek
advice from your own appropriately authorized independent financial advisor.
 
N M Rothschild & Sons Limited ("Rothschilds") is acting for Atlantic Richfield
Company ("ARCO") and ARCO Irish Holdings Inc. ("ARCO Irish Holdings") in
relation to the Final Offer and no one else, and will not be responsible to
anyone other than ARCO and ARCO Irish Holdings for providing the protections
afforded to customers of Rothschilds nor for providing advice in relation to
the Final Offer. Rothschilds is acting through Rothschild Inc. for the purpose
of making the Final Offer in the United States.
 
If you have sold or otherwise transferred all your American Depositary Shares
("Aran ADSs") of Aran Energy plc ("Aran"), please pass this document and all
accompanying documents as soon as possible to the purchaser or transferee, or
to the bank, stockbroker or other agent through whom the sale or transfer was
effected for transmission to the purchaser or transferee. However, such
documents should not be distributed, forwarded or transmitted in or into
Australia, Canada or Japan.
 
This Revised Letter should be read in conjunction with the offer document
dated August 25, 1995 (the "Original Offer Document") and the accompanying
final offer document dated October 9, 1995 (together with the disclosure
document dated October 9, 1995, the "Final Offer Document"). The definitions
used in the Original Offer Document and Final Offer Document also apply, where
the context requires, in this Revised Letter.
 
- -------------------------------------------------------------------------------
 
                         REVISED LETTER OF TRANSMITTAL
           TO ACCEPT THE FINAL OFFER FOR AMERICAN DEPOSITARY SHARES
                   EVIDENCED BY AMERICAN DEPOSITARY RECEIPTS
                                      OF
                                ARAN ENERGY plc
          PURSUANT TO THE FINAL OFFER DOCUMENT DATED OCTOBER 9, 1995
                                      BY
                         N M ROTHSCHILD & SONS LIMITED
                                 ON BEHALF OF
                           ARCO IRISH HOLDINGS INC.
                      (A WHOLLY OWNED SUBSIDIARY OF ARCO)
 
- --------------------------------------------------------------------------------
 THE FINAL OFFER IS OPEN FOR ACCEPTANCE UNTIL 1:00 P.M. (DUBLIN AND LONDON
 TIME), 9:00 A.M. (NEW YORK CITY TIME), ON OCTOBER 24, 1995 (THE "INITIAL
 PERIOD") UNLESS EXTENDED (IN ACCORDANCE WITH THE TERMS THEREOF). AT THE
 CONCLUSION OF THE INITIAL PERIOD OR ON OR BEFORE THE CONCLUSION OF ANY
 EXTENSION THEREOF AND ON THE SATISFACTION OR, WHERE PERMITTED, WAIVER OF
 THE CONDITION(S) TO THE FINAL OFFER, THE PURCHASE OF ALL ARAN SECURITIES
 IN RESPECT OF WHICH THE FINAL OFFER HAS BEEN VALIDLY ACCEPTED AND NOT
 WITHDRAWN WILL TAKE PLACE, AND THE FINAL OFFER WILL BE EXTENDED FOR A
 SUBSEQUENT PERIOD OF AT LEAST FOURTEEN CALENDAR DAYS. PRIOR TO THE FINAL
 OFFER BECOMING OR OTHERWISE BEING DECLARED UNCONDITIONAL IN ALL RESPECTS,
 ACCEPTING ARAN SECURITYHOLDERS WILL HAVE THE RIGHT TO WITHDRAW THEIR
 ACCEPTANCES IN RESPECT THEREOF. HOWEVER, IN THE EVENT OF THE FINAL OFFER
 BECOMING OR BEING DECLARED UNCONDITIONAL IN ALL RESPECTS, NO RIGHTS OF
 WITHDRAWAL WILL BE AVAILABLE TO ACCEPTING ARAN SECURITYHOLDERS IN THE
 SUBSEQUENT PERIOD DURING WHICH THE FINAL OFFER REMAINS OPEN FOR
 ACCEPTANCE. ACCEPTANCES SHOULD BE DISPATCHED AS SOON AS POSSIBLE AND IN
 ANY EVENT SO AS TO BE RECEIVED NOT LATER THAN 1:00 P.M. (DUBLIN AND LONDON
 TIME), 9:00 A.M. (NEW YORK CITY TIME) ON OCTOBER 24, 1995.
- --------------------------------------------------------------------------------
 
                  TO: FIRST CHICAGO TRUST COMPANY OF NEW YORK
                                 US DEPOSITARY 
      By Mail:            By Facsimile Transmission               By Hand or 
                      (for Eligible Institutions only):       Overnight Courier:
                              
     Suite 4660           Fax: (201) 222-4720 or 4721            Suite 4680
    P.O. Box 2559                                              14 Wall Street
Jersey City, NJ 07303        For Information Call:              Eighth Floor
                                                             New York, NY 10005
                          (800) 659-6111 (Toll Free)        
                                      or
                                (201) 324-0137
<PAGE>
 
   DELIVERY OF THIS REVISED LETTER OF TRANSMITTAL TO AN ADDRESS, OR
TRANSMISSION OF INSTRUCTIONS VIA A FACSIMILE OR TELEX NUMBER, OTHER THAN AS
SET FORTH ABOVE, DOES NOT CONSTITUTE A VALID DELIVERY.
 
   THE INSTRUCTIONS ACCOMPANYING THIS REVISED LETTER OF TRANSMITTAL SHOULD BE
READ CAREFULLY BEFORE THIS REVISED LETTER OF TRANSMITTAL IS COMPLETED.
 
   ACCEPTING HOLDERS OF ARAN ADSs WILL RECEIVE PAYMENT IN DOLLARS INSTEAD OF
IRISH POUNDS UNLESS THEY ELECT OTHERWISE HEREIN TO RECEIVE PAYMENT IN IRISH
POUNDS OR POUNDS STERLING. IF YOU WISH TO RECEIVE IRISH POUNDS INSTEAD OF
DOLLARS YOU MUST PLACE A "X" IN THE BOX ENTITLED "IRISH POUNDS PAYMENT
ELECTION." IF YOU WISH TO RECEIVE POUNDS STERLING INSTEAD OF DOLLARS YOU MUST
PLACE A "X" IN THE BOX ENTITLED "POUNDS STERLING PAYMENT ELECTION."
 
   ACCEPTANCE OF THE FINAL OFFER IN RESPECT OF ARAN SHARES (EXCEPT INSOFAR AS
THEY ARE REPRESENTED BY ARAN ADSs) CANNOT BE MADE BY MEANS OF THIS REVISED
LETTER OF TRANSMITTAL. If you hold Aran shares that are not represented by
Aran ADSs, you can obtain a Form of Acceptance for accepting the Final Offer
in respect of those Aran shares from the Irish Receiving Agent, the US
Depositary and the UK Receiving Agent. See Instruction 13 of this Revised
Letter of Transmittal.
 
   Delivery of a Revised Letter of Transmittal, Aran American Depositary
Receipts evidencing Aran ADSs ("Aran ADRs") (or book-entry transfer of such
Aran ADSs) and any other required documents to the US Depositary by Aran ADSs
holders will be deemed (without any further action by the US Depositary) to
constitute an acceptance of the Final Offer by such holder with respect to
such Aran ADSs subject to the terms and conditions set out in the Final Offer
Document and this Revised Letter of Transmittal. Capitalised terms and certain
other terms used in this Revised Letter of Transmittal and not otherwise
defined herein shall have the respective meanings assigned to them in the
Final Offer Document and, as applicable, the Original Offer Document.
 
   Holders of Aran ADSs who wish to accept the Final Offer should use (i)
either this Revised Letter of Transmittal or the Letter of Transmittal
accompanying the Original Offer Document and (ii) if such tendering holders
wish to use the guaranteed delivery procedures set forth in the Final Offer,
either the Revised Notice of Guaranteed Delivery or the Notice of Guaranteed
Delivery accompanying the Original Offer Document. TENDERS OF ARAN ADSs
PURSUANT TO THE LETTER OF TRANSMITTAL ACCOMPANYING THE ORIGINAL OFFER DOCUMENT
SHALL BE DEEMED TO CONSTITUTE AN ACCEPTANCE OF THE FINAL OFFER IN RESPECT OF
ALL SUCH ADSs AT THE APPLICABLE PRICE DETERMINED AS DESCRIBED IN THE FINAL
OFFER DOCUMENT. THIS REVISED LETTER OF TRANSMITTAL PERMITS A TENDERING HOLDER
OF ARAN ADSs TO ELECT, BY COMPLETING THE APPROPRIATE BOX(ES) BELOW, EITHER (i)
TO ACCEPT THE FINAL OFFER IN RESPECT OF ALL OR SOME OF SUCH HOLDER'S ARAN ADSs
AT THE APPLICABLE PRICE DETERMINED AS DESCRIBED IN THE FINAL OFFER DOCUMENT,
(ii) TO ACCEPT THE FINAL OFFER ONLY IF THE STATOIL/CONNEMARA PROPOSAL (BEING
THE PROPOSED FARM-OUT OF AN AGGREGATE 47.5% INTEREST IN THE CONNEMARA LEASE
UNDERTAKING BY ARAN SERVICING LIMITED TO STATOIL (U.K.) LIMITED ("STATOIL"))
IS VOTED DOWN BY THE ARAN SHAREHOLDERS AT THE EXTRAORDINARY GENERAL MEETING OF
ARAN SHAREHOLDERS CONVENED FOR OCTOBER 23, 1995 OR AT ANY ADJOURNMENT THEREOF
(THE "ARAN MEETING") (I.E., ONLY AT THE HIGHER PRICE) OR ONLY IF THE
STATOIL/CONNEMARA PROPOSAL IS APPROVED (I.E., ONLY AT THE LOWER PRICE) OR
(iii) TO ACCEPT THE FINAL OFFER IN RELATION TO A DIFFERENT NUMBER OF ARAN ADSs
DEPENDING ON WHETHER THE STATOIL/CONNEMARA PROPOSAL IS OR IS NOT APPROVED BY
THE ARAN SHAREHOLDERS AT THE ARAN MEETING.
 
  Withdrawals of previous tenders of Aran ADSs pursuant to Letters of
Transmittal may be made in writing or by facsimile transmission to the U.S.
Depositary at the addresses and facsimile copy number set forth below in
accordance with the procedures set forth in the Final Offer Document and the
Original Offer Document. Delivery of a properly completed and duly executed
Revised Letter of Transmittal in accordance with the procedures set forth in
the Final Offer Document and the Original Offer Document will automatically
constitute a revocation of any Letter of Transmittal previously delivered by
the tendering Aran ADS holder.
 
   This Revised Letter of Transmittal is to be used either if Aran ADRs
evidencing Aran ADSs are to be forwarded herewith or if delivery of Aran ADSs
is to be made by book-entry transfer to an account maintained by the US
Depositary at a Book-Entry Transfer Facility as defined in and pursuant to the
procedures for book-entry transfer set forth in "Acceptance Procedures for
Holders of Aran ADSs--Book-Entry Transfer Facilities" in Part B of Appendix 1
to the Original Offer Document, as amended, as applicable, by the Final Offer
Document. Holders of Aran ADSs who deliver a Revised Notice of Guaranteed
Delivery to accept the Final Offer must, inter alia, effect the deliveries
described below within three trading days after the execution of such Revised
Notice.
<PAGE>
 
[_] CHECK BOX IF ARAN ADSs IN RESPECT OF WHICH THE FINAL OFFER IS BEING
    ACCEPTED ARE BEING DELIVERED BY BOOK-ENTRY TRANSFER MADE TO AN ACCOUNT
    MAINTAINED BY THE US DEPOSITARY WITH A BOOK-ENTRY TRANSFER FACILITY AND
    COMPLETE THE FOLLOWING (ONLY PARTICIPANTS IN A BOOK-ENTRY TRANSFER
    FACILITY MAY DELIVER ARAN ADSs BY BOOK-ENTRY TRANSFER):
 
    Name of Delivering Institution ____________________________
 
    Check box opposite name of relevant Book-Entry Transfer Facility:
 
    [_] The Depositary Trust Company
 
    [_] Midwest Securities Trust Company
 
    [_] Philadelphia Depositary Trust Company
 
    Account Number __________       Transaction Code Number _______
 
    If a holder of Aran ADSs wishes to accept the Final Offer and Aran ADRs
evidencing such ADSs are not immediately available or the procedures for book-
entry transfer cannot be completed on a timely basis, or if time will not
permit all required documents to reach the US Depositary prior to the expiry
of the Final Offer, such holder's acceptance of the Final Offer may
nevertheless be effected using the guaranteed delivery procedures. See
"Acceptance Procedures for Holders of Aran ADSs--Guaranteed delivery
procedures" in Part B of Appendix 1 to the Original Offer Document, as
amended, as applicable, by the Final Offer Document. See Instruction 2 of this
Letter of Transmittal. HOWEVER, RECEIPT OF A REVISED NOTICE OF GUARANTEED
DELIVERY WILL NOT BE TREATED AS A VALID ACCEPTANCE FOR THE PURPOSE OF
SATISFYING THE ACCEPTANCE CONDITION.
 
[_] CHECK BOX ONLY IF ARAN ADSs IN RESPECT OF WHICH THE OFFER IS BEING
    ACCEPTED ARE BEING DELIVERED PURSUANT TO A REVISED NOTICE OF GUARANTEED
    DELIVERY PREVIOUSLY SENT TO THE US DEPOSITARY AND COMPLETE THE FOLLOWING:
 
    Name(s) of registered owner(s) ____________________
 
    Date of execution of Revised Notice of Guaranteed Delivery _________________
 
    Name of Institution that guaranteed delivery _________
 
    IF DELIVERY BY BOOK-ENTRY TRANSFER CHECK BOX:
 
    [_] The Depository Trust Company
    [_] Midwest Securities Trust Company
    [_] Philadelphia Depository Trust Company
 
    Account Number __________       Transaction Code ________
<PAGE>
 
  IN CONNECTION WITH THE DELIVERY OF THIS REVISED LETTER OF TRANSMITTAL, (i)
BOX 1 OR (ii) BOX 2 AND/OR BOX 3 SHOULD BE COMPLETED. IT IS IMPORTANT THAT YOU
READ THE FOLLOWING INSTRUCTIONS CAREFULLY BEFORE COMPLETING THE APPROPRIATE
BOX(ES). PLEASE NOTE THAT, IF YOU SUBMIT THIS REVISED LETTER OF TRANSMITTAL,
DULY EXECUTED, AND FAIL TO MAKE ANY ELECTION REGARDING THE BASIS ON WHICH YOU
ARE ACCEPTING THE FINAL OFFER, YOU WILL BE DEEMED TO HAVE ACCEPTED THE FINAL
OFFER IN RESPECT OF ALL ARAN ADSs TENDERED HEREBY AT THE APPLICABLE PRICE
DETERMINED AS DESCRIBED IN THE FINAL OFFER DOCUMENT.
 
- --------------------------------------------------------------------------------
                    INSTRUCTIONS FOR BOXES 1, 2 AND 3 BELOW
   IN ADDITION TO SIGNING THIS REVISED LETTER OF TRANSMITTAL IN THE SPACE
 PROVIDED HEREIN FOR SUCH SIGNATURE(S) AND COMPLYING WITH ALL OTHER
 INSTRUCTIONS CONTAINED HEREIN, PLEASE COMPLY WITH THE FOLLOWING WITH
 RESPECT TO BOXES 1, 2 AND 3 BELOW:
 1. IF YOU WISH TO ACCEPT THE FINAL OFFER IN RESPECT OF THE SAME NUMBER OF
    ARAN ADSs WHETHER OR NOT THE STATOIL/CONNEMARA PROPOSAL IS APPROVED,
    COMPLETE BOX 1 WITH, AMONG OTHER THINGS, THE NUMBER OF ARAN ADSs IN
    RESPECT OF WHICH YOU WISH TO ACCEPT THE FINAL OFFER. IN SUCH CASE, DO
    NOT COMPLETE BOXES 2 AND 3.
 2. IF YOU WISH TO ACCEPT THE FINAL OFFER ONLY IF THE STATOIL/CONNEMARA
    PROPOSAL IS NOT APPROVED, COMPLETE BOX 2 WITH, AMONG OTHER THINGS, THE
    NUMBER OF ARAN ADSs IN RESPECT OF WHICH YOU WISH TO ACCEPT THE FINAL
    OFFER.
 3. IF YOU WISH TO ACCEPT THE FINAL OFFER ONLY IF THE STATOIL/CONNEMARA
    PROPOSAL IS APPROVED, COMPLETE BOX 3 WITH, AMONG OTHER THINGS, THE
    NUMBER OF ARAN ADSs IN RESPECT OF WHICH YOU WISH TO ACCEPT THE FINAL
    OFFER.
 4. IF YOU WISH TO ACCEPT THE FINAL OFFER IN RELATION TO A DIFFERENT
    NUMBER OF ARAN ADSs DEPENDING ON WHETHER THE STATOIL/CONNEMARA
    PROPOSAL IS OR IS NOT APPROVED, (i) COMPLETE BOX 2 WITH, AMONG OTHER
    THINGS, THE NUMBER OF ARAN ADSs IN RESPECT OF WHICH YOU WISH TO ACCEPT
    THE FINAL OFFER IF THE STATOIL/CONNEMARA PROPOSAL IS NOT APPROVED AND
    (ii) COMPLETE BOX 3 WITH, AMONG OTHER THINGS, THE NUMBER OF ARAN ADSs
    IN RESPECT OF WHICH YOU WISH TO ACCEPT THE FINAL OFFER IF THE
    STATOIL/CONNEMARA PROPOSAL IS APPROVED.

 INCOMPLETE OR INACCURATE ACCEPTANCES: IF YOU DO NOT INSERT A NUMBER IN
 ANY OF BOXES 1, 2 OR 3 YOU WILL BE DEEMED TO HAVE ACCEPTED THE FINAL
 OFFER IN RESPECT OF YOUR ENTIRE REGISTERED HOLDING OF ARAN ADSs WHETHER
 OR NOT THE STATOIL/CONNEMARA PROPOSAL IS APPROVED. IF YOU INSERT IN ANY
 OF BOXES 1, 2 OR 3 A NUMBER GREATER THAN YOUR ENTIRE REGISTERED HOLDING
 OF ARAN ADSs, YOU WILL BE DEEMED TO HAVE INSERTED INSTEAD THE NUMBER
 EQUAL TO YOUR ENTIRE REGISTERED HOLDING.

<TABLE>
<CAPTION> 
- --------------------------------------------------------------------------------------------------------
BOX 1              ACCEPTANCE OF FINAL OFFER WHETHER OR NOT
                  THE STATOIL/CONNEMARA PROPOSAL IS APPROVED
 -------------------------------------------------------------------------------------------------------
                         DESCRIPTION OF ACCEPTING ADSs
- --------------------------------------------------------------------------------------------------------

  INSERT NAME(S) AND ADDRESS(ES) OF                               ACCEPTING ADSs
  REGISTERED HOLDER(S)                                (ATTACH ADDITIONAL LIST IF NECESSARY)
- --------------------------------------------------------------------------------------------------------
  <S>                                 <C>                    <C>                    <C>
                                      ACCEPTING ADR          TOTAL NUMBER OF        NUMBER OF ACCEPTING
                                      SERIAL NUMBER(S)*      ACCEPTING ADSs         ADSs**
                                                             EVIDENCED BY ADRs*
                          ------------------------------------------------------------------------------
                          ------------------------------------------------------------------------------
                          ------------------------------------------------------------------------------
========================================================================================================
BOX 2                             ACCEPTANCE OF FINAL OFFER 
                          IF THE STATOIL/CONNEMARA PROPOSAL IS NOT APPROVED
- --------------------------------------------------------------------------------------------------------
                               DESCRIPTION OF ACCEPTING ADSs
- --------------------------------------------------------------------------------------------------------
  INSERT NAME(S) AND ADDRESS(ES) OF                               ACCEPTING ADSs
  REGISTERED HOLDER(S)                                (ATTACH ADDITIONAL LIST IF NECESSARY)
- -------------------------------------------------------------------------------------------------------
  <S>                                 <C>                    <C>                    <C>
                                      ACCEPTING ADR          TOTAL NUMBER OF        NUMBER OF ACCEPTING
                                      SERIAL NUMBER(S)*      ACCEPTING ADSs         ADSs**
                                                             EVIDENCED BY ADRs*
                          -----------------------------------------------------------------------------
                          -----------------------------------------------------------------------------
                          -----------------------------------------------------------------------------
=======================================================================================================
BOX 3                            ACCEPTANCE OF FINAL OFFER
                      IF THE STATOIL/CONNEMARA PROPOSAL IS APPROVED
- -------------------------------------------------------------------------------------------------------
                             DESCRIPTION OF ACCEPTING ADSs
- -------------------------------------------------------------------------------------------------------
  INSERT NAME(S) AND ADDRESS(ES) OF                               ACCEPTING ADSs
  REGISTERED HOLDER(S)                                (ATTACH ADDITIONAL LIST IF NECESSARY)
- -------------------------------------------------------------------------------------------------------
  <S>                                 <C>                    <C>                    <C>
                                      ACCEPTING ADR          TOTAL NUMBER OF        NUMBER OF ACCEPTING
                                      SERIAL NUMBER(S)*      ACCEPTING ADSs         ADSs**
                                                             EVIDENCED BY ADRs*
                          -----------------------------------------------------------------------------
                          -----------------------------------------------------------------------------
                          -----------------------------------------------------------------------------
=======================================================================================================
</TABLE> 
  * Need not be completed by Book-Entry Securityholders.
 ** Unless otherwise indicated, it will be assumed that the Final Offer is being
    accepted in respect of all Aran ADSs delivered to the US Depositary. See
    Instruction 4.
 
<PAGE>
 
                    NOTE: SIGNATURES MUST BE PROVIDED BELOW
              PLEASE READ THE ACCOMPANYING INSTRUCTIONS CAREFULLY
 
Ladies and Gentlemen:
 
   The undersigned hereby instructs the US Depositary to accept the Final
Offer on behalf of the undersigned with respect to the Aran ADSs (which
expression in this Revised Letter of Transmittal shall, except where the
context otherwise requires, be deemed to include, without limitation, the Aran
shares represented thereby) specified in the applicable box(es) entitled
"Description of Accepting ADSs", subject to the terms and conditions set forth
in the Original Offer Document, the Final Offer Document and this Revised
Letter of Transmittal, by informing ARCO Irish Holdings in writing that the
Final Offer has been so accepted. The undersigned hereby acknowledges that
delivery of this Revised Letter of Transmittal, the Aran ADSs evidencing
tendered Aran ADSs (or book-entry transfer of such Aran ADSs) and any other
required documents to the US Depositary by a holder of Aran ADSs will be
deemed (without any further action by the US Depositary) to constitute
acceptance of the Final Offer by such holder in respect of such holder's Aran
ADSs, subject to the terms and conditions set out in the Original Offer
Document, the Final Offer Document and this Revised Letter of Transmittal.
 
   The undersigned understands that acceptance of the Final Offer by the
undersigned pursuant to the procedures described herein and in the
instructions hereto will constitute a binding agreement between the
undersigned and ARCO Irish Holdings upon the terms and subject to the
conditions of the Final Offer. IF ACCEPTANCE HAS BEEN MADE IN RESPECT OF THE
ARAN ADSs THEN A SEPARATE ACCEPTANCE IN RESPECT OF THE ARAN SHARES REPRESENTED
BY SUCH ARAN ADSs MAY NOT BE MADE.
 
   The undersigned hereby delivers to the US Depositary the above-described
Aran ADSs for which the Final Offer is being accepted, in accordance with the
terms and conditions of the Original Offer Document, the Final Offer Document
and this Revised Letter of Transmittal, receipt of which is hereby
acknowledged.
 
   Upon the terms of the Final Offer (including, if the Final Offer is
extended, revised or amended, the terms or conditions of any such extension,
revision or amendment), and effective at the time that the conditions to the
Final Offer have been satisfied or, where permitted, waived (at which time
ARCO Irish Holdings will give notice thereof to the US Depositary), the
undersigned hereby sells, assigns and transfers to, or upon the order of, ARCO
Irish Holdings all right, title and interest in and to all Aran ADSs with
respect to which the Final Offer is being accepted (and any and all Aran ADSs
or other securities or rights issuable in respect of such Aran ADSs) and
irrevocably constitutes and appoints the US Depositary the true and lawful
agent and attorney-in-fact of the undersigned with respect to such Aran ADSs
(and any such other Aran ADSs, securities or rights), with full power of
substitution (such power of attorney being deemed to be an irrevocable power
coupled with an interest), to (a) deliver ADRs for such Aran ADSs (and any
such other Aran ADSs, securities or rights) or accept transfer of ownership of
such Aran ADSs (and any such other Aran ADSs, securities or rights) on the
account books maintained by a Book-Entry Transfer Facility together, in any
such case, with all accompanying evidences of transfer and authenticity to, or
upon the order of, ARCO Irish Holdings, (b) present such Aran ADRs (and any
other Aran ADSs, securities or rights) for transfer, and (c) receive all
benefits and otherwise exercise all rights of beneficial ownership of such
Aran ADSs (and any such other Aran ADSs, securities or rights), all in
accordance with the terms of the Final Offer.
 
   The undersigned agrees that its execution hereof (together with any
signature guarantees) and its delivery to the US Depositary shall constitute
an authority to any director of ARCO Irish Holdings or Rothschilds and to ARCO
Irish Holdings or Rothschilds and/or their respective agents in accordance
with the terms of Section 7 of Part B of Appendix l of the Original Offer
Document (Revised Offer and Reduction of the Acceptance Condition), as
amended, as applicable, by the Final Offer Document.
 
   The undersigned agrees that effective from and after the date hereof or, if
later, the date on which the Final Offer becomes unconditional (or if the
Final Offer will become unconditional or lapse immediately upon the outcome of
the resolution in question or in such other circumstances as ARCO Irish
Holdings may request and the Panel may permit), (a) ARCO Irish Holdings or its
agents shall be entitled to direct the exercise of any votes attaching to the
Aran Shares represented by any Aran ADSs in respect of which the Final Offer
has been accepted or is deemed to have been accepted (the "Accepting ADSs")
and any or all other rights and privileges attaching to such Aran ADSs,
including any right to requisition the convening of a general meeting or
separate class meeting of Aran, and (b) the execution of this Revised Letter
of Transmittal by a holder of Aran ADSs (together with any signature
guarantees) and its delivery to the US Depositary shall constitute in respect
of Accepting ADSs (i) an authority to Aran or its agents from the undersigned
to send any notice, circular, warrant, document or other communications that
may be required to be sent to him or her as an Aran ADS holder to ARCO Irish
Holdings at its principal office, (ii) an authority to ARCO Irish Holdings or
any director of ARCO Irish Holdings or any person appointed by such person for
such purpose to sign any consent to short notice of a general meeting or
separate class meeting on behalf of the holder of Accepting ADSs and/or to
execute a form of proxy in respect of the Accepting ADSs appointing any person
nominated by ARCO Irish Holdings to attend general meetings and separate class
meetings of Aran and any adjournment thereof and to exercise the votes
attaching to the Aran shares represented by such Accepting ADSs on his or her
behalf, such votes to
<PAGE>
 
be cast (where relevant) so far as possible to satisfy or to assist directly
or indirectly in satisfying any outstanding condition of the Final Offer,
(iii) the agreement of the undersigned not to exercise any such rights without
the consent of ARCO Irish Holdings and the irrevocable undertaking of the
undersigned not to appoint a proxy for or to attend general meetings or
separate class meetings of Aran in respect of such Accepting ADSs, (iv)
confirmation that the undersigned (1) has not received or sent copies of this
Revised Letter of Transmittal or any related document in, into or from
Australia, Canada or Japan, (2) is accepting the Final Offer from outside
Australia, Canada and Japan, (3) is not an agent or fiduciary acting on a non-
discretionary basis for a principal, unless such agent or fiduciary is an
authorised employee of such principal or such principal has given any
instructions with respect to the Final Offer from outside Australia, Canada
and Japan and (4) is entitled to sell and transfer the beneficial ownership of
the Accepting ADSs and that such Accepting ADSs are sold fully paid and free
from all liens, equitable interests, charges, and encumbrances and together
with all rights attaching thereto since (and including) August 21, 1995
including voting rights and the right to all dividends and other distributions
declared, made or paid on or after August 21, 1995.
 
   The undersigned hereby represents and warrants that the undersigned has
full power and authority to accept the Final Offer and to sell, assign and
transfer the Aran ADSs (and the Aran shares represented by such Aran ADSs) in
respect of which the Final Offer is being accepted or deemed to be accepted
(and any and all other Aran ADSs, securities or rights issued or issuable in
respect of such Aran ADSs) and, when the same are purchased by ARCO Irish
Holdings, ARCO Irish Holdings will acquire good title thereto, free from all
liens, equitable interests, charges, and encumbrances and together with all
rights attaching thereto, including voting rights and the right to receive all
dividends and other distributions declared, made or paid on or after August
21, 1995 with respect to the Aran shares represented by the Aran ADSs. The
undersigned will, upon request, execute any additional documents deemed by the
US Depositary or ARCO Irish Holdings to be necessary or desirable to complete
the sale, assignment and transfer of the Aran ADSs in respect of which the
Final Offer is being accepted (and any and all other Aran ADSs, securities or
rights).
 
   All authority herein conferred or agreed to be conferred pursuant to this
Revised Letter of Transmittal shall be binding upon the successors, assigns,
heirs, executors, administrators and legal representatives of the undersigned
and shall not be affected by, and shall survive, the death or incapacity of
the undersigned. Except as stated herein, in the Original Offer Document and
the Final Offer Document, this acceptance is irrevocable.
 
   Unless otherwise indicated herein under "Special Payment Instructions", the
undersigned hereby instructs the US Depositary to issue, or cause to be
issued, the check for the purchase price in the name(s) of the registered
holder(s) appearing under "Description of Accepting ADSs" in Box(es) 1, 2
and/or 3 above, as applicable. Similarly, unless otherwise indicated under
"Special Delivery Instructions", the undersigned hereby instructs the US
Depositary to mail, or cause to be mailed, the checks for the purchase price
and/or return, or cause to be returned, any Aran ADRs evidencing Aran ADSs in
respect of which the Final Offer is not being accepted (and accompanying
documents, as appropriate) to the address(es) of the registered holder(s)
appearing under "Description of Accepting ADSs" in Boxes 1, 2 and/or 3, as
applicable. In the event that the "Special Payment Instructions" and/or the
"Special Delivery Instructions" are completed, the undersigned hereby
instructs the US Depositary to issue and/or mail, or cause to be issued and/or
mailed, the checks for the purchase price, if any, in the name of, and to, the
person or persons so indicated. In the case of a book-entry delivery of Aran
ADSs, the undersigned hereby instructs the US Depositary to credit the account
maintained at the Book-Entry Transfer Facility indicated above with any Aran
ADSs not accepted for payment.
 
   If neither the Box headed "Irish Pounds Payment Election" nor the Box
headed "Pounds Sterling Payment Election" is checked, the undersigned hereby
instructs the US Depositary to convert all amounts payable pursuant to the
Final Offer from Irish pounds to U.S. dollars at the noon buying rate in
London for cable transfers prevailing on the latest practicable business day
preceding the dispatch of payment as certified by The Royal Bank of Scotland
plc and to pay such amounts by check payable in U.S. dollars. The actual
amount of U.S. dollars or pounds sterling received will depend upon the
exchange rate prevailing on the latest practicable date preceding the date on
which payment is made by ARCO Irish Holdings. Aran securityholders should also
be aware that the exchange rate which is prevailing at the date on which the
undersigned executes this Revised Letter of Transmittal may be different from
that on the date of despatch of payment by ARCO Irish Holdings. In all cases,
fluctuations in the US dollar/Irish pound and pounds sterling/Irish pounds
exchange rates are at the risk of accepting Aran securityholders who do not
elect to receive their consideration in Irish pounds. Such currency exchange
will be effected by the US Depositary on behalf of the requesting Aran
securityholder and ARCO Irish Holdings shall have no responsibility or
obligation with respect thereto.
 
   SUBJECT TO THE TERMS OF THE ORIGINAL OFFER DOCUMENT AND THE FINAL OFFER
DOCUMENT, THIS REVISED LETTER OF TRANSMITTAL SHALL NOT BE CONSIDERED COMPLETE
AND VALID, AND PAYMENT OF CONSIDERATION PURSUANT TO THE FINAL OFFER SHALL NOT
BE MADE, UNTIL THE ARAN ADRs EVIDENCING THE ARAN ADSs IN RESPECT OF WHICH THE
FINAL OFFER IS BEING ACCEPTED AND ALL OTHER REQUIRED DOCUMENTATION HAVE BEEN
RECEIVED BY THE US DEPOSITARY AS PROVIDED IN THE ORIGINAL OFFER DOCUMENT, THE
FINAL OFFER DOCUMENT AND THIS REVISED LETTER OF TRANSMITTAL.
<PAGE>
 
- --------------------------------------------------------------------------------
 
                                   SIGN HERE
            (ALSO COMPLETE SUBSTITUTE FORM W-9 ON LAST PAGE OF TEXT)
     ______________________________________________________________

     ______________________________________________________________
                           (Signature(s) of Owner(s))
 
     Dated: _______________________________________________________
 
     (Must be signed by registered holder(s) exactly as name(s)
     appear(s) on Aran ADR(s) evidencing the Aran ADS(s) or by
     person(s) to whom Aran ADR(s) surrendered have been assigned
     and transferred, as evidenced by endorsement, stock powers
     and other documents transmitted herewith. If signature is by
     any trustee, executor, administrator, guardian, attorney-in-
     fact, officer of a corporation or others acting in a
     fiduciary or representative capacity, please set forth the
     following and see Instruction 5.)
     Name(s) ______________________________________________________

     ______________________________________________________________
                                 (Please Print)

     Capacity (Full Title) ________________________________________

     Address ______________________________________________________

     ______________________________________________________________
                              (Including Zip Code)
 
     Area Code and Telephone No. __________________________________

     Employer Identification No.
     or Social Security No. _______________________________________
 
                           GUARANTEE OF SIGNATURE(S)
                           (SEE INSTRUCTIONS 1 AND 5)

     Authorised Signature _________________________________________

     Name _________________________________________________________
                                 (Please Print)

     Name of Firm _________________________________________________

     Address ______________________________________________________

     ______________________________________________________________
                              (Including Zip Code)
 
     Area Code and Telephone No. __________________________________

     Dated: _______________________________________________________

- --------------------------------------------------------------------------------
<PAGE>
 
- -----------------------------------------------------------------------------
   [_] CHECK HERE IF ANY OF THE ARAN ADRs REPRESENTING ARAN ADSs THAT YOU
       OWN HAVE BEEN LOST, STOLEN OR DESTROYED AND SEE INSTRUCTION 12.
 
       Number of Aran ADSs represented by the lost, stolen or destroyed Aran
       ADRs:_________
- ----------------------------------------------------------------------------- 

- -----------------------------------   -----------------------------------
    SPECIAL PAYMENT INSTRUCTIONS        SPECIAL DELIVERY INSTRUCTIONS
  (SEE INSTRUCTIONS 1, 5, 6 AND 7)     (SEE INSTRUCTIONS 1, 5, 6 AND 7)
  
   [_] Check box ONLY if the check      Check boxes ONLY if the check
   for the purchase price for           for the purchase price for
   Aran ADSs accepted for               Aran ADSs accepted for
   payment is to be issued in           payment and/or the Aran ADRs
   the name of someone other            for any Aran ADSs with
   than the undersigned.                respect to which the Final
                                        Offer is not being accepted
                                        or which are accepted for
                                        payment are to be sent to
                                        someone other than the
                                        undersigned, or to the
                                        undersigned at an address
                                        other than that shown above.
 
                                        Mail [_] Check
                                             [_] ADRs to: 

   Name _________________________        Name _________________________
   (Please Print: First, Middle and      (Please Print: First, Middle and
   Last Name)                            Last Name)
   Address ______________________        Address ______________________

   ------------------------------        ------------------------------
        (Including Zip Code)                  (Including Zip Code) 
   (Employer Identification or                
   Social Security No.) _________        
- ----------------------------------    -----------------------------------
 
 
                    ---------------------------------
                         POUNDS STERLING OR IRISH
                         POUNDS PAYMENT ELECTION
                           (SEE INSTRUCTION 8)
 
                      Check appropriate Box below
                      ONLY if you wish to receive
                      all (but not part) of the
                      amounts to be paid by a check
                      or checks in pounds sterling
                      or Irish pounds. If you do
                      not check a Box, you will
                      receive payment by a check or
                      checks in US dollars. If you
                      check the "Irish Pounds
                      Payment Election" Box, you
                      will receive the Irish pound
                      amounts payable to you. If
                      you do not check either Box
                      or you check the "Pounds
                      Sterling Payment Election"
                      box, ARCO Irish Holdings will
                      arrange for the conversion of
                      the Irish pound amounts
                      payable to you to US dollars
                      or pounds sterling, as the
                      case may be, at the noon
                      buying rate in London for
                      transfers in Irish pounds
                      prevailing on the latest
                      practicable business day
                      preceding the dispatch of
                      payment as certified by The
                      Royal Bank of Scotland plc.
 
                      [_] Pounds Sterling Payment
                          Election
 
                      [_] Irish Pounds Payment
                          Election
                    --------------------------------- 
<PAGE>

                                  INSTRUCTIONS
 
          FORMING PART OF THE TERMS AND CONDITIONS OF THE FINAL OFFER
 
   1. GUARANTEE OF SIGNATURES. No signature guarantee is required on the
Revised Letter of Transmittal if (a) the Revised Letter of Transmittal is
signed by the registered holder(s) of the Aran ADSs in respect of which the
Final Offer is being accepted herewith and such holder(s) have not completed
either the Box entitled "Special Payment Instructions" or the Box entitled
"Special Delivery Instructions" on this Revised Letter of Transmittal or (b)
such Aran ADSs are accepted for the account of an Eligible Institution. In all
other cases, all signatures on this Revised Letter of Transmittal must be
guaranteed by a financial institution (including most banks, savings and loan
associations and brokerage houses) which is a participant in the Securities
Transfer Agents Medallion Program, the New York Stock Exchange Medallion
Program, or the Stock Exchange Medallion Program (an "Eligible Institution").
See Instruction 5.
 
   If the Aran ADSs are registered in the name of a person other than the
signatory of the Revised Letter of Transmittal, then the Aran ADRs evidencing
the Aran ADSs in respect of which the Final Offer is being accepted must be
endorsed or accompanied by appropriate stock powers, signed exactly as the
name or names of the registered owner or owners appear on the Aran ADRs, with
the signatures on such Aran ADRs or stock powers guaranteed as aforesaid. See
Instruction 5.
 
   2. DELIVERY OF REVISED LETTER OF TRANSMITTAL AND ADSs. This Revised Letter
of Transmittal is to be completed by holders either if Aran ADRs evidencing
Aran ADSs are to be forwarded herewith or if delivery is to be made by book-
entry transfer to an account maintained by the US Depositary at a Book-Entry
Transfer Facility pursuant to the procedures for book-entry transfer set out
in "Acceptance Procedures for Holders of Aran ADSs--Book-Entry Transfer
Facilities" in Part B of Appendix 1 to the Original Offer Document, as
amended, as applicable, by the Final Offer Document. Aran ADRs evidencing Aran
ADSs or confirmation of any book-entry transfer into the US Depositary's
account at a Book-Entry Transfer Facility of Aran ADSs delivered
electronically, as well as a properly completed and duly executed Letter of
Transmittal or Revised Letter of Transmittal (or facsimiles thereof), together
with any required signature guarantees and any other documents required by
this Revised Letter of Transmittal, must be delivered to the US Depositary at
one of its addresses set forth herein.
 
   Aran ADS holders whose Aran ADRs are not immediately available or who
cannot deliver their Aran ADRs and all other required documents to the US
Depositary or complete the procedures for book-entry transfer on a timely
basis may accept the Final Offer prior to the Final Offer having lapsed or
expired with respect to their Aran ADSs by properly completing and duly
executing the Revised Notice of Guaranteed Delivery or the Notice of
Guaranteed Delivery accompanying the Original Offer Document pursuant to the
guaranteed delivery procedures set out in "Acceptance Procedures for Holders
of Aran ADSs--Guaranteed delivery procedures" in Part B of Appendix 1 to the
Original Offer Document, as amended, as applicable, by the Final Offer
Document. Pursuant to the guaranteed delivery procedures, such holder's
acceptance of the Final Offer may nevertheless be effected if all of the
following conditions are satisfied: (a) acceptance is made by or through an
Eligible Institution; (b) a properly completed and duly executed Revised
Notice of Guaranteed Delivery or the Notice of Guaranteed Delivery
accompanying the Original Offer Document substantially in the form provided by
ARCO Irish Holdings is received by the US Depositary, as provided for in the
Final Offer Document, prior to the Final Offer having expired; and (c) the
Aran ADRs evidencing the Aran ADSs in respect of which the Final Offer is
being accepted (or, in the case of Aran ADSs held in book-entry form, timely
confirmation of the book-entry transfer of such Aran ADSs into the US
Depositary's account at a Book-Entry Transfer Facility as described in the
Original Offer Document, as amended, as applicable, by the Final Offer
Document) together with a properly completed and duly executed Revised Letter
of Transmittal (or facsimile thereof) with any required signature guarantees
and any other documents required by this Revised Letter of Transmittal, are
received by the US Depositary within three trading days after the date of
execution of such Revised Notice of Guaranteed Delivery or Notice of
Guaranteed Delivery. For these purposes, a "trading day" is any day on which
NASDAQ is open for business.
 
   THE REVISED NOTICE OF GUARANTEED DELIVERY OR THE NOTICE OF GUARANTEED
DELIVERY ACCOMPANYING THE ORIGINAL OFFER DOCUMENT MAY BE DELIVERED BY HAND TO
THE US DEPOSITARY OR TRANSMITTED BY FACSIMILE TRANSMISSION OR MAILED TO THE US
DEPOSITARY AND MUST INCLUDE A SIGNATURE GUARANTEE BY AN ELIGIBLE INSTITUTION
IN THE FORM SET OUT IN SUCH REVISED NOTICE OF GUARANTEED DELIVERY OR NOTICE OF
GUARANTEED DELIVERY. THE METHOD OF DELIVERY OF ARAN ADSs AND ALL OTHER
REQUIRED DOCUMENTS IS AT THE OPTION AND RISK OF THE HOLDERS OF ARAN ADSs
ACCEPTING THE FINAL OFFER. IF DELIVERY IS BY MAIL, REGISTERED MAIL WITH RETURN
RECEIPT REQUESTED, PROPERLY INSURED, IS RECOMMENDED. IN ALL CASES, SUFFICIENT
TIME SHOULD BE ALLOWED TO ENSURE TIMELY DELIVERY.
 
   RECEIPT OF A REVISED NOTICE OF GUARANTEED DELIVERY OR A NOTICE OF
GUARANTEED DELIVERY ACCOMPANYING THE ORIGINAL OFFER DOCUMENT WILL NOT BE
TREATED AS A VALID ACCEPTANCE FOR THE PURPOSE OF SATISFYING THE ACCEPTANCE
CONDITION. TO BE COUNTED TOWARDS SATISFACTION OF THIS CONDITION, PRIOR TO THE
FINAL OFFER HAVING
<PAGE>
 
EXPIRED, THE ARAN ADRs EVIDENCING ARAN ADSs REFERRED TO IN THE REVISED NOTICE
OF GUARANTEED DELIVERY OR THE NOTICE OF GUARANTEED DELIVERY ACCOMPANYING THE
ORIGINAL OFFER DOCUMENT MUST HAVE BEEN RECEIVED BY THE US DEPOSITARY OR, IN
THE CASE OF ARAN ADSs HELD IN BOOK-ENTRY FORM, TIMELY CONFIRMATION OF A BOOK-
ENTRY TRANSFER OF SUCH ARAN ADSs INTO THE US DEPOSITARY'S ACCOUNT AT A BOOK-
ENTRY TRANSFER FACILITY PURSUANT TO THE PROCEDURES SET OUT IN THE ORIGINAL
OFFER DOCUMENT, AS AMENDED, AS APPLICABLE, BY THE FINAL OFFER DOCUMENT, MUST
HAVE BEEN RECEIVED BY THE US DEPOSITARY, IN EITHER CASE, TOGETHER WITH A DULY
EXECUTED REVISED LETTER OF TRANSMITTAL OR THE LETTER OF TRANSMITTAL
ACCOMPANYING THE ORIGINAL OFFER DOCUMENT (OR FACSIMILES THEREOF) WITH ANY
REQUIRED SIGNATURE GUARANTEES AND ANY OTHER REQUIRED DOCUMENTS.
 
   No alternative, conditional or contingent acceptance will be accepted and
no fractional Aran ADSs will be purchased. All Accepting ADS holders, by
execution of this Revised Letter of Transmittal (or facsimile thereof), waive
any right to receive any notice of the acceptance of their Aran ADSs for
payment.
 
   3. INADEQUATE SPACE. If the space provided herein is inadequate, the serial
numbers of the certificates and/or the number of Aran ADSs should be listed on
a separate schedule attached hereto.
 
   4. PARTIAL ACCEPTANCES. If the Final Offer is to be accepted in respect of
less than all of the Aran ADSs evidenced by any Aran ADRs delivered to the US
Depositary herewith, fill in the number of Aran ADSs in respect of which the
Final Offer is being accepted in the section entitled "Number of Accepting
ADSs" under "Delivery of Accepting ADSs" in Box(es) 1, 2 and/or 3 above, as
applicable. In such case, in the event of the Final Offer becoming
unconditional, a new Aran ADR for the remainder of the Aran ADSs (in respect
of which the Final Offer is not being accepted) represented by the old Aran
ADR will be sent to the registered holder (or delivered to the person signing
the Revised Letter of Transmittal or in accordance with such person's
instructions as such person properly indicates thereon) as promptly as
practicable following the date on which the Aran ADSs in respect of which the
Final Offer has been accepted are purchased.
 
   The Final Offer will be deemed to have been accepted in respect of all Aran
ADSs evidenced by Aran ADRs delivered to the US Depositary unless otherwise
indicated. In the case of partial acceptances, Aran ADSs in respect of which
the Final Offer was not accepted will not be reissued to a person other than
the registered holder of the released Aran ADR.
 
   5. SIGNATURES ON REVISED LETTER OF TRANSMITTAL, STOCK POWERS AND
ENDORSEMENTS. If this Revised Letter of Transmittal is signed by the
registered holder(s) of the Aran ADSs in respect of which the Final Offer is
being accepted hereby, the signature(s) must correspond with the name(s) as
written on the face of the certificates without any change whatsoever.
 
   If any of the Aran ADSs in respect of which the Final Offer is being
accepted hereby are owned of record by two or more owners, all such owners
must sign this Revised Letter of Transmittal.
 
   If any of the Aran ADSs in respect of which the Final Offer is being
accepted are registered in different names on different Aran ADRs, it will be
necessary to complete, sign and submit as many separate Revised Letters of
Transmittal as there are different registrations of Aran ADRs.
 
   If this Revised Letter of Transmittal or any Aran ADRs or stock powers are
signed by trustees, executors, administrators, guardians, attorneys-in-fact,
officers of corporations or others acting in a fiduciary or representative
capacity, such persons should so indicate when signing, and proper evidence
satisfactory to ARCO Irish Holdings of their authority so to act must be
submitted.
 
   When this Revised Letter of Transmittal is signed by the registered
holder(s) of the Aran ADSs listed and transmitted hereby, no endorsements of
certificates or separate stock powers are required unless payment of the
purchase price is to be issued to a person other than the registered
holder(s). Signatures on such Aran ADRs or stock powers must be guaranteed by
an Eligible Institution.
 
   If this Revised Letter of Transmittal is signed by a person other than the
registered holder(s) of the Aran ADSs listed and transmitted hereby, the Aran
ADRs must be endorsed or accompanied by appropriate stock powers signed
exactly as the names(s) of the registered holder(s) appear(s) on the Aran ADRs
evidencing such Aran ADSs. Signatures on such Aran ADRs or stock powers must
be guaranteed by an Eligible Institution.
 
   6. STOCK TRANSFER TAXES. ARCO Irish Holdings will pay or cause to be paid
any stock transfer taxes with respect to the transfer and sale to it or its
order of Aran ADSs pursuant to the Final Offer. If, however, payment of the
purchase price is to be made to any persons other than the registered
holder(s), or if Aran ADSs in respect of which the Final Offer is being
accepted are registered in the name of any person other than the person(s)
signing this
<PAGE>
 
Revised Letter of Transmittal, the amount of any stock transfer taxes (whether
imposed on the registered holder(s) or such person(s)) payment on account of
the transfer to such person(s) will be deducted from the purchase price unless
satisfactory evidence of the payment of such taxes or exemption therefrom is
submitted.
 
   Except as provided in this Instruction 6, it will not be necessary for
transfer tax stamps to be affixed to the Aran ADRs listed in this Revised
Letter of Transmittal.
 
   7. SPECIAL PAYMENT AND DELIVERY INSTRUCTIONS. If the check for the purchase
price is to be issued in the name of a person other than the signer of this
Revised Letter of Transmittal or if the check for the purchase price is to be
sent and/or any Aran ADRs evidencing Aran ADSs in respect of which the Final
Offer is not being accepted are to be returned to a person other than the
signer of this Revised Letter of Transmittal or to an address other than that
shown on the reverse, the Boxes labelled "Special Payment Instructions" and/or
"Special Delivery Instructions" on this Revised Letter of Transmittal should
be completed.
 
   8. POUNDS STERLING OR IRISH POUNDS PAYMENT ELECTION. If the checks for the
purchase price are to be issued in pounds sterling or Irish pounds, please
check the appropriate Box marked either "Pounds Sterling Payment Election" or
"Irish Pounds Payment Election". If you do not check either of such Boxes or
you check the "Pounds Sterling Payment Election" Box, all Irish pound amounts
payable pursuant to the Final Offer will be converted by the US Depositary
into US dollars or pounds sterling (as appropriate) at the noon buying rate
prevailing in London for transfers in Irish pounds on the latest practicable
business day preceding the despatch of payment as certified by The Royal Bank
of Scotland plc.
 
   9. WAIVER OF CONDITIONS. ARCO Irish Holdings reserves the absolute right in
its sole discretion to waive any of the specified conditions of the Final
Offer, in whole or in part, in the case of any Aran ADSs accepted to the
extent permitted by applicable law and the rules of the City Code.
 
   10. 31% U.S. BACK-UP WITHHOLDING. In order to avoid "back-up withholding" of
U.S. Federal income tax on any cash payment received upon the surrender of
Aran ADSs pursuant to the Final Offer, an Aran ADS holder must, unless an
exemption applies, provide the US Depositary with his correct Taxpayer
Identification Number ("TIN") on Substitute Form W-9 on either this Revised
Letter of Transmittal or the Letter of Transmittal accompanying the Original
Offer Document and certify, under penalties of perjury, that such number is
correct and that he is not subject to back-up withholding. If the correct TIN
is not provided a $50 penalty may be imposed by the Internal Revenue Service
and cash payments made in exchange for the surrendered Aran ADSs may be
subject to back-up withholding of 31%.
 
   Back-up withholding is not an additional U.S. Federal income tax. Rather,
the U.S. Federal income tax liability of persons subject to back-up
withholding will be reduced by the amount of such tax withheld. If back-up
withholding results in an overpayment of taxes, a refund may be applied for
from the Internal Revenue Service.
 
   The TIN that is to be provided on the Substitute Form W-9 is that of the
registered holder(s) of the Aran ADSs or of the last transferee appearing on
the transfers attached to, or endorsed on, the Aran ADSs. The TIN for an
individual is his social security number. The box in Part 2 of the Substitute
Form W-9 may be checked, if the person surrendering the Aran ADSs has not been
issued a TIN and has applied for a TIN or intends to apply for a TIN in the
near future. If the box in Part 2 is checked, the person surrendering the Aran
ADSs must also complete the Certificate of Awaiting Taxpayer Identification
Number below. Notwithstanding that the box in Part 2 is checked (and the
Certificate of Awaiting Taxpayer Identification Number is completed), the US
Depositary will withhold 31% on any cash payment of the purchase price for the
Aran ADSs made prior to the time it is provided with a properly certified TIN.
 
   Exempt persons (including among others, corporations) are not subject to
back-up withholding. A foreign individual or foreign entity may qualify as an
exempt person by submitting a statement (on Form W-8), signed under penalties
of perjury, certifying such person's foreign status. Form W-8 can be obtained
from the US Depositary. An Aran ADS holder should consult his tax advisor as
to his qualification for an exemption from back-up withholding and the
procedure for obtaining such exemption.
 
   For additional guidance, see the enclosed Guidelines for Certification of
Taxpayer Identification Number on Substitute Form W-9.
 
   11. REQUESTS FOR ASSISTANCE OR ADDITIONAL COPIES. Questions and requests for
assistance or additional copies of the Final Offer Document, this Revised
Letter of Transmittal, the Revised Notice of Guaranteed Delivery and the
Guidelines for Certification of Taxpayer Identification Number on Substitute
Form W-9 may be directed to the
<PAGE>
 
US Depositary at the address and telephone number set forth above or the Irish
Receiving Agent or the UK Receiving Agent at the appropriate address and
telephone number set forth in the Final Offer Document.
 
   12. LOST, DESTROYED OR STOLEN CERTIFICATES. If any Aran ADR evidencing Aran
ADSs has been lost, destroyed or stolen, the holder thereof should promptly
notify the US Depositary by checking the box immediately preceding the special
payment/special delivery instructions and indicating the number of Aran ADSs
evidenced by such lost, destroyed or stolen Aran ADRs. The holder thereof will
then be instructed as to the steps that must be taken in order to replace such
Aran ADRs. This Revised Letter of Transmittal and related documents cannot be
processed until the procedures for replacing lost, destroyed or stolen Aran
ADRs have been followed.
 
   13. HOLDERS OF ARAN SHARES NOT REPRESENTED BY ARAN ADSs. Holders of Aran
shares have been sent a revised Form of Acceptance with the Final Offer
Document and may not accept the Final Offer in respect of Aran shares pursuant
to this Revised Letter of Transmittal except in so far as those shares are
represented by Aran ADSs. If any holder of Aran shares which are not
represented by Aran ADSs needs to obtain a copy of a revised Form of
Acceptance, such holder should contact the Irish Receiving Agent or the UK
Receiving Agent at the appropriate address and telephone number set forth in
the Final Offer Document or the US Depositary at the address and telephone
number set forth above. HOLDERS OF ARAN ADSs MUST USE A REVISED LETTER OF
TRANSMITTAL OR A LETTER OF TRANSMITTAL ACCOMPANYING THE ORIGINAL OFFER
DOCUMENT TO TENDER THEIR ARAN ADSs.
<PAGE>
 
             PAYER'S NAME: FIRST CHICAGO TRUST COMPANY OF NEW YORK
 
- --------------------------------------------------------------------------------
                    PART 1 - PLEASE PROVIDE YOUR TIN
                    IN THE BOX AT RIGHT AND CERTIFY
                    BY SIGNING AND DATING BELOW
 
                  -----------------------------------
 
                    CERTIFICATION - UNDER THE            Social Security Number
                    PENALTIES OF PERJURY, I CERTIFY      or Employer
                    THAT:                                Identification Number
     
                                                            
                    1. The number shown on this form        _______________
                       is my correct taxpayer          _________________________
                       identification number (or I
                       am waiting for a number to be
                       issued to me), and
                    2. I am not subject to back-up
                       withholding because (a) I am
                       exempt from back-up
                       withholding or (b) I have not
                       been notified by the Internal
                       Revenue Service ("IRS") that
                       I am subject to back-up
                       withholding as a result of a
                       failure to report all
                       interest or dividends, or (c)
                       the IRS has notified me that
                       I am no longer subject to
                       back-up withholding.
            
                  -----------------------------------
                    Certification Instructions - you
                    must cross out item 2 above if
                    you have been notified by the
                    IRS that you are currently
                    subject to back-up withholding
                    because of underreporting
                    interest or dividends on your
                    tax return.

                    NAME ............................
SUBSTITUTE                     (Please Print)
Form W-9            ADDRESS .........................
Department of
the Treasury        .................................
Internal                     (include Zip Code)
Revenue Service
                    
Payer's Request     SIGNATURE ......... DATE ........
Taxpayer for
Identification                                                    Part 2
Number (TIN)                                                [_] Awaiting TIN

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

 YOU MUST COMPLETE THE FOLLOWING CERTIFICATION 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 (a) 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 (b) I intend to mail or deliver
   an application in the near future. I understand that,
   notwithstanding that I have checked the box in Part 2 (and have
   completed this Certificate of Awaiting Taxpayer Identification
   Number), all reportable payments made to me prior to the time I
   provide the US Depositary with a properly certified taxpayer
   identification number will be subject to a 31% back-up withholding
   tax.

   Signature ..............................     Date ...................
- --------------------------------------------------------------------------------

   NOTE: FAILURE TO COMPLETE AND RETURN THIS SUBSTITUTE FORM W-9 MAY
         RESULT IN BACK-UP WITHHOLDING OF 31% OF ANY CASH PAYMENT MADE
         TO YOU. PLEASE REVIEW THE ENCLOSED GUIDELINES FOR
         CERTIFICATION OF TAXPAYER IDENTIFICATION NUMBER ON SUBSTITUTE
         FORM W-9 FOR ADDITIONAL DETAILS
 
                   The US Depositary for the Final Offer is:
 
                         First Chicago Trust Company of
                                    New York
                      Call: (800) 659-6111 (Toll Free) or
                                 (201) 324 0137
 
   Suite 4680                                                Suite 4660
   14 Wall Street                                         P.O. Box 2559
   Eighth Floor                                   Jersey City, NJ 07303
   New York, NY 10005
 
                 The US Dealer Manager for the Final Offer is:
 
                                Rothschild Inc.
                          1251 Avenue of The Americas
                                   51st Floor
                               New York, NY 10020
                      (212) 403-3611 within New York City
           (800) 753-5151 ext. 3611 (Toll Free) outside New York City
<PAGE>
 
 
 
 
                      [THIS PAGE INTENTIONALLY LEFT BLANK]
 

<PAGE>

                                                                 EXHIBIT (a)(20)

THIS DOCUMENT IS IMPORTANT AND REQUIRES YOUR IMMEDIATE ATTENTION. If you are in
any doubt about the action you should take, you are recommended to seek advice
from your own appropriately authorised independent financial adviser.
 
N M Rothschild & Sons Limited is acting for Atlantic Richfield Company ("ARCO")
and ARCO Irish Holdings Inc. ("ARCO Irish Holdings") in connection with the
Final Offer and no one else and will not be responsible to anyone other than
ARCO and ARCO Irish Holdings for providing the protections afforded to
customers of N M Rothschild & Sons Limited nor for providing advice in relation
to the Final Offer. N M Rothschild & Sons Limited is acting through Rothschild
Inc. for the purposes of making the Final Offer in the United States.
 
If you have sold or otherwise transferred all your shares in Aran Energy plc
("Aran"), please pass this document, all accompanying documents and (where
applicable) the accompanying reply-paid envelope as soon as possible to the
purchaser or transferee, or to the bank, stockbroker or other agent through
whom the sale or transfer was effected, for transmission to the purchaser or
transferee. HOWEVER, THIS FORM OF ACCEPTANCE SHOULD NOT BE DISTRIBUTED,
FORWARDED OR TRANSMITTED IN OR INTO AUSTRALIA, CANADA, OR JAPAN.
 
This Form should be read in conjunction with the accompanying Final Offer
document dated 9 October 1995 from Rothschilds (the "Final Offer document").
The definitions used in the offer document dated 25 August 1995 (the "Original
Offer document") and the Final Offer document also apply, where the context
requires, in this Form.
- --------------------------------------------------------------------------------
 
                   FORM OF ACCEPTANCE, AUTHORITY AND ELECTION
 
                                FINAL CASH OFFER
 
                                       BY
 
                         N M ROTHSCHILD & SONS LIMITED
 
                                  ON BEHALF OF
 
                        ARCO IRISH HOLDINGS INC. [LOGO]

                      TO ACQUIRE THE ENTIRE SHARE CAPITAL
 
                                       OF
 
                                ARAN ENERGY plc
 
- --------------------------------------------------------------------------------
 
                               ACTION TO BE TAKEN
 
 .  Please read pages 2 and 4 of this Form, where detailed instructions on how
   to complete this Form and accept the Final Offer in respect of your Aran
   shares are set out, and complete and sign page 3, in the presence of a
   witness (who should also sign where indicated).
 
                                    AND THEN
 
   return this Form, duly completed and signed, together with your share
   certificate(s) and/or other document(s) of title, either by hand or by post
   to AIB Bank, Registrars' & New Issue Department, Bankcentre, P.O. Box 954,
   Ballsbridge, Dublin 4 or The Royal Bank of Scotland plc, Registrar's
   Department, New Issues Section, P.O. Box 859, Consort House, East Street,
   Bedminster, Bristol BS99 1XZ or by hand only to The Royal Bank of Scotland
   plc, Registrar's Department, New Issues Section, 67 Lombard Street, London
   EC3P 3DL or, by post to First Chicago Trust Company of New York, Suite
   4660, P.O. Box 2559, Jersey City, NJ 07303 or by hand or overnight courier
   to First Chicago Trust Company of New York, Suite 4680, 14 Wall Street,
   Eighth Floor, New York, NY 10005 AS SOON AS POSSIBLE, AND IN ANY EVENT SO
   AS TO BE RECEIVED BY NOT LATER THAN 1.00 P.M. (DUBLIN AND LONDON TIME),
   9.00 A.M. (NEW YORK CITY TIME) ON 24 OCTOBER 1995. A REPLY-PAID ENVELOPE IS
   ENCLOSED FOR YOUR USE IF YOU HAVE A REGISTERED ADDRESS IN THE REPUBLIC OF
   IRELAND OR THE UNITED KINGDOM.
 
 .  If you are sending this document to First Chicago Trust Company of New York
   you should refer to the discussion of US back-up withholding requirements in
   paragraph 12 of Appendix 4 to the Original Offer document.
 
 .  If your share certificate(s) and/or other document(s) of title is/are with
   your bank, stockbroker or other agent, you should complete and sign this
   Form and arrange for it to be lodged by such agent with the relevant
   document(s).
 
 .  If your share certificate(s) and/or other document(s) of title is/are not
   readily available, the Form should nevertheless be signed and returned as
   stated above and the share certificate(s) and/or other document(s) of title
   forwarded as soon as possible thereafter to AIB Bank, The Royal Bank of
   Scotland plc or, if appropriate, First Chicago Trust Company of New York, at
   any of the addresses given above.
 
 .  The provisions of Appendix 1 of the Final Offer document are deemed to be
   incorporated in, and form part of, this Form and should be read in
   conjunction with this Form.
 
 .  If you hold Aran shares jointly with others, you must arrange for your co-
   holders to sign this Form.
 
IF YOU HAVE ANY QUESTIONS AS TO HOW TO COMPLETE THIS FORM, PLEASE TELEPHONE AIB
BANK IN DUBLIN ON 01 660 0311 (EXT. 12280), THE ROYAL BANK OF SCOTLAND plc IN
BRISTOL ON 0117 937 0666 OR FIRST CHICAGO TRUST COMPANY OF NEW YORK IN THE US
ON (800) 659 6111 (TOLL FREE) OR (201) 324 0137.
<PAGE>
 
                                     Page 2
 
                           How to complete this Form
THIS FORM MAY NOT BE USED TO ACCEPT THE FINAL OFFER IN RESPECT OF ARAN ADSs.
Holders of Aran ADSs wishing to accept the Final Offer in respect of such
securities should complete a Letter of Transmittal and any of the documents
related thereto if applicable. Copies of these documents may be obtained from
AIB Bank, The Royal Bank of Scotland plc or First Chicago Bank of New York at
the appropriate address on the front cover of this Form.
 
- --------------------------------------------------------------------------------
 
          PLEASE FOLLOW THE INSTRUCTIONS BELOW WHEN COMPLETING PAGE 3.
 
[1] TO ACCEPT THE FINAL OFFER FOR YOUR ARAN SHARES
 
    IF YOU WISH TO ACCEPT THE FINAL OFFER IN RESPECT OF THE SAME
    NUMBER OF SHARES WHETHER THE STATOIL/CONNEMARA PROPOSAL IS
    APPROVED OR NOT, INSERT IN BOX [1] THE TOTAL NUMBER OF ARAN
    SHARES FOR WHICH YOU WISH TO ACCEPT AND LEAVE BOX [1A] AND BOX
    [1B] BLANK.

    YOU MUST ALSO SIGN BOX [2] IN THE PRESENCE OF A WITNESS,
    WHICH WILL CONSTITUTE YOUR ACCEPTANCE OF THE FINAL OFFER, AND
    COMPLETE BOX [3]. YOU SHOULD ALSO COMPLETE BOXES [4] AND/OR
    [5], [6] OR [7] AS APPROPRIATE.

                                 OR                                    ICON   
                                                                     INDICATING
    (I) IF YOU WISH TO ACCEPT THE FINAL OFFER ONLY IF THE             TO "SEE  
        STATOIL/CONNEMARA PROPOSAL IS NOT APPROVED, INSERT IN        NEXT PAGE" 
        BOX [1A] THE NUMBER OF SHARES IN RESPECT OF WHICH YOU WISH
        TO ACCEPT.
   (II) IF YOU WISH TO ACCEPT THE FINAL OFFER ONLY IF THE
        STATOIL/CONNEMARA PROPOSAL IS APPROVED, INSERT IN BOX
        [1B] THE NUMBER OF SHARES IN RESPECT OF WHICH YOU WISH TO
        ACCEPT.
  (III) IF YOU WISH TO VARY THE NUMBER OF ARAN SHARES IN RESPECT
        OF WHICH YOU WISH TO ACCEPT THE FINAL OFFER DEPENDING ON  
        THE OUTCOME OF THE STATOIL/CONNEMARA PROPOSAL, INSERT IN  
        BOX [1A] THE NUMBER OF SHARES IN RESPECT OF WHICH YOU    
        WISH TO ACCEPT IF THE STATOIL/CONNEMARA IS NOT APPROVED   
        AND INSERT IN BOX [1B] THE NUMBER OF SHARES IN RESPECT
        OF WHICH YOU WISH TO ACCEPT IF IT IS APPROVED.

  IN EACH CASE, YOU MUST ALSO SIGN BOX [2] IN THE PRESENCE OF A
  WITNESS WHICH WILL CONSTITUTE YOUR ACCEPTANCE OF THE FINAL
  OFFER, AND COMPLETE BOX [3]. YOU SHOULD ALSO COMPLETE
  BOXES [4] AND/OR [5], [6] OR [7] AS APPROPRIATE.
 
  INCOMPLETE OR INACCURATE ACCEPTANCES: IF YOU SIGN BOX [2] AND
  DO NOT INSERT A NUMBER IN ANY OF BOXES [1], [1A] OR [1B] YOU
  WILL BE DEEMED TO HAVE ACCEPTED THE FINAL OFFER IN RESPECT OF
  YOUR ENTIRE REGISTERED HOLDING OF ARAN SHARES WHETHER OR NOT
  THE STATOIL/CONNEMARA PROPOSAL IS APPROVED. IF YOU INSERT IN
  ANY OF BOXES [1], [1A] OR [1B] A NUMBER GREATER THAN YOUR
  ENTIRE REGISTERED HOLDING OF ARAN SHARES, YOU WILL BE DEEMED TO
  HAVE INSERTED INSTEAD THE NUMBER EQUAL TO YOUR ENTIRE
  REGISTERED HOLDING.
 
  NOTE: BY COMPLETING BOX [2], YOU APPOINT A DIRECTOR OF
  ROTHSCHILDS AS YOUR REPRESENTATIVE (IF YOU ARE A BODY
  CORPORATE) OR YOUR ATTORNEY (IF YOU ARE AN INDIVIDUAL) TO
  ATTEND, SPEAK AND VOTE ON YOUR BEHALF AT THE ARAN EGM TO BE
  HELD ON 23 OCTOBER 1995. THIS APPOINTMENT IS MADE IN ACCORDANCE
  WITH, AS APPROPRIATE, PART B OF APPENDIX 1 TO THE FINAL OFFER
  DOCUMENT, ARTICLE 75 OF THE ARTICLES OF ASSOCIATION OF ARAN AND
  SECTION 139 OF THE IRISH COMPANIES ACT.
 
 YOUR ACCEPTANCE SHOULD BE RECEIVED AS SOON AS POSSIBLE AND IN ANY EVENT BY NOT
 LATER THAN 1.00 P.M. (DUBLIN AND LONDON TIME), 9.00 A.M. (NEW YORK CITY TIME)
                              ON 24 OCTOBER 1995.
 
- --------------------------------------------------------------------------------
[2] SIGNATURES
    ----------  
 
    YOU MUST SIGN                 applicable, a corporation
    BOX [2] REGARDLESS OF         may execute this Form as
    WHICH OTHER BOX(ES) YOU       a deed in any manner
    COMPLETE.                     permitted by the laws of
                                  the territory in which
    IN THE CASE OF JOINT          the corporation is
    HOLDERS ALL SUCH HOLDERS      incorporated for the
    MUST SIGN.                    execution of this Form as
                                  a deed.
    YOU MUST SIGN IN THE                                                ICON   
    PRESENCE OF A WITNESS,        If this Form is not                INDICATING
    WHO SHOULD ALSO SIGN          signed by the registered            TO "SEE  
    WHERE INDICATED, AND GIVE     holder(s), insert the              NEXT PAGE"
    DETAILS OF HIS/HER NAME,      name(s) and capacity
    ADDRESS AND OCCUPATION.       (e.g. executor(s)), of
    THE WITNESS MUST NOT BE       the person(s) signing
    ANOTHER JOINT HOLDER AND      this Form. You should
    MUST BE OVER EIGHTEEN.        also deliver evidence of
                                  your authority in
    A corporation must            accordance with the notes
    execute under seal, the       on page 4 of this Form.
    seal being affixed and     
    witnessed in accordance       This Form shall take      
    with its Articles of          effect as a Deed executed 
    Association or other          by you and by any joint   
    regulations.                  holder(s).                 
    Alternatively, where     

- --------------------------------------------------------------------------------
[3] FULL NAME(S) AND ADDRESS
    ------------------------
 
    Complete Box [3] with         CAPITALS, and provide a
    the full name and address     daytime telephone number
    of the sole or first-         whereupon you may be
    named registered holder       contacted in the event of
    together with the names       any query.
    of all other joint
    holders (if any) in BLOCK
- --------------------------------------------------------------------------------
[4] ALTERNATIVE ADDRESS
    -------------------
 
    If you want the               your bank manager or
    consideration and other       stockbroker), you should
    documents to be sent to       also complete Box [4] in
    someone other than the        BLOCK CAPITALS with an
    first-named registered        address outside
    holder at the address set     Australia, Canada or
    out in Box [3] (e.g.          Japan.
- --------------------------------------------------------------------------------
[5] IRISH POUNDS PAYMENT ELECTION
    -----------------------------
 
    Accepting Aran                put a "X" in Box [5];
    shareholders with             otherwise you will
    registered addresses in       receive payment in pounds
    the UK who wish to            sterling (unless you
    receive payment of all        elect to receive US
    (but not part) of the         dollars -- see Box [7]).
    consideration to be paid
    in Irish pounds,

    NOTE: SEE PARAGRAPH 12 ON PAGES 19 AND 20 OF THE FINAL OFFER DOCUMENT FOR
    FURTHER INFORMATION ON THE CURRENCY ELECTIONS.
- --------------------------------------------------------------------------------
[6] POUNDS STERLING PAYMENT ELECTION
    -------------------------------- 
 
    Accepting Aran                on the Irish pounds Final
    shareholders with             Offer price) into pounds
    registered addresses          sterling at the noon
    outside the UK who wish       buying rate prevailing in
    to receive payment of all     London for transfers in
    (but not part) of the         Irish pounds on the
    consideration to be paid      latest practicable
    in pounds sterling, put a     business day preceding
    "X" in Box [6];               the date of despatch of
    otherwise you will            payment as certified by
    receive payment in Irish      The Royal Bank of
    pounds (unless you elect      Scotland plc. All costs
    to receive US dollars --      of such conversion will
    see Box [7]). If you put      be paid by ARCO Irish
    a "X" in Box [7], ARCO        Holdings.
    Irish Holdings will
    arrange for the
    conversion of the
    consideration payable to
    you (based

    NOTE: SEE PARAGRAPH 12 ON PAGES 19 AND 20 OF THE FINAL OFFER DOCUMENT FOR
    FURTHER INFORMATION ON THE CURRENCY ELECTIONS.
- --------------------------------------------------------------------------------
[7] US DOLLARS PAYMENT ELECTION
    ---------------------------  
 
    Any accepting Aran            consideration payable to
    shareholders who wish to      you (based on the Irish
    receive payment of all        pounds Final Offer price)
    (but not part) of the         into US dollars at the
    consideration to be paid      noon buying rate
    in US dollars, put a "X"      prevailing in London for
    in Box [7]; otherwise         transfers in Irish pounds
    (unless you specify           on the latest practicable
    differently in Box [5]        business day preceding
    or Box [6]) you will          the date of despatch of
    automatically receive         payment as certified by
    payment in Irish pounds       The Royal Bank of
    or, if you have a             Scotland plc. All costs
    registered address in the     of such conversion will
    UK, pounds sterling. If       be paid by ARCO Irish
    you put a "X" in              Holdings.
    Box [7], ARCO Irish
    Holdings will arrange for
    the conversion of the
 
    NOTE: SEE PARAGRAPH 12 ON PAGES 19 AND 20 OF THE FINAL OFFER DOCUMENT FOR
    FURTHER INFORMATION ON THE CURRENCY ELECTIONS.
- --------------------------------------------------------------------------------
<PAGE>
 
                                    Page 3

Please complete as explained on pages 2 and 4
================================================================================
[1] To accept the Final Offer
    Complete Box [1] if you wish to accept the Final Offer in respect of the
    same number of Aran shares whether or not the Statoil/Connemara proposal is
    approved. Then complete Box [3] and sign Box [2] in the presence of a
    witness who should sign and give details of his/her name, address and
    occupation where indicated.
 
                                               Box [1]
                          ---------------------------- 
                            No. of Aran shares_______
                          ----------------------------
 
  If instead you wish to accept the Final Offer in respect of some or all of
  your Aran shares on a basis which depends upon whether or not the
  Statoil/Connemara proposal is approved, you should read carefully the
  Guidance Notes on page 2 which set out how you should complete Box [1A]
  and/or Box [1B]. Then complete Box [3] and sign Box [2] in the
  presence of a witness who should sign and give details of his/her name,
  address and occupation where indicated.
 
                           Box [1A]                          Box [1B]
       ----------------------------      ----------------------------
        No. of Aran shares________        No. of Aran shares________
       ----------------------------      ----------------------------
 
  Please also complete Boxes [4] and/or [5], [6], or [7] if appropriate. PLEASE
  READ CAREFULLY THE INSTRUCTIONS OPPOSITE BOXES [5], [6], AND [7] ON PAGE 2
  REGARDING THE CURRENCY IN WHICH YOU WILL RECEIVE YOUR CONSIDERATION.
================================================================================
[2] Sign here to accept the Final Offer                                  Box [2]

             ---------------------------------------------------------
             SIGNED AS A DEED AND DELIVERED BY/EXECUTED AS A DEED BY:
 
             1. Signature of holder_____   3. Signature of holder ____
             in the presence of:           in the presence of:
             (Witness) name ____________   (Witness) name ____________
             Address ___________________   Address ___________________
             Occupation ________________   Occupation ________________
             Signature of witness ______   Signature of witness ______

             2. Signature of holder ____   4. Signature of holder ____
             in the presence of:           in the presence of:
             (Witness) name ____________   (Witness) name ____________
             Address ___________________   Address ___________________
             Occupation ________________   Occupation ________________
             Signature of witness ______   Signature of witness ______
             =========================================================
                                           Director __________________
             For use by a corporation      Signature _________________
             Executed as a Deed by _____   Director/Secretary ________
             ___________________________   Signature _________________
             (name of corporation)
             ---------------------------------------------------------  
================================================================================
[3] Full name(s) and address                                             Box [3]
 
             ------------------------------------------------------------ 
               First-named registered       Joint registered holders
                       holder
 
 
 
              1. Forename(s)               2. Forename(s)
              ---------------------------  ---------------------------
              (Mr, Mrs, Ms, Miss or        (Mr, Mrs, Ms, Miss or
              Title)                       Title)

              Surname                      Surname
              ---------------------------  ---------------------------
              Address                      3. Forename(s)
              ---------------------------  ---------------------------
              ---------------------------  (Mr, Mrs, Ms, Miss or
              ---------------------------  Title)

              Postcode                     Surname
              ---------------------------  ---------------------------
                                           4. Forename(s)
 
                                           ---------------------------
                                           (Mr, Mrs, Ms, Miss or
                                           Title)

                                           Surname
                                           ---------------------------
            ------------------------------------------------------------
             Please give a daytime telephone number where you may be
             contacted in the event of a query. Tel.:
================================================================================
[4] Address to which consideration and                                   Box [4]
    other document(s) are to be sent if
    not your own (to be completed in block
    capitals)

IRISH REGISTERED SHAREHOLDERS WHO WISH   --------------------------------
TO RECEIVE PAYMENT IN IRISH POUNDS          Name _____________________
SHOULD NOT COMPLETE ANY OF BOXES         
[5], [6] OR [7]                           Address __________________
                                            __________________________
                                            Postcode _________________
                                          --------------------------------
================================================================================
[5] If you have a registered address in the UK and wish to receive payment in
    Irish pounds, put a "X" in Box [5]. Unless you have marked this Box or
    Box [7], you will receive pounds sterling.
                                                                      Box 5 [_]
================================================================================
[6] If you have a registered address outside the UK and wish to receive payment
    in pounds sterling, put a "X" in Box [6]. Unless you have marked this Box
    or Box [7], you will receive Irish pounds.
                                                                      Box 6 [_]
================================================================================
[7] If you wish to receive payment in US dollars, put a "X" in Box [7]
                                                                      Box 7 [_]
================================================================================

For office use only
- ------------------- 
H
- ------------------- 
C
- ------------------- 
Q
- ------------------- 
 
 
- --------------------------------------------------------------------------------
FOR USE BY REGISTRARS/STOCK EXCHANGE
 
- ------------------------------------------------------------------------------- 
 
 
 
<PAGE>
 
                                    Page 4

        FURTHER NOTES REGARDING THE COMPLETION AND LODGING OF THIS FORM
 
In order to avoid delay and inconvenience to yourself, the following points
may assist you.
 
1. IF A HOLDER IS AWAY FROM HOME (E.G. ABROAD OR ON HOLIDAY)

   Send this Form by the quickest means (e.g. air mail) to the holder for
   execution (but not into Australia, Canada or Japan) or, if he has executed
   a power of attorney, have this Form signed by the attorney in the presence
   of a witness. In the latter case, the original power of attorney (or a copy
   thereof duly certificated in accordance with the Powers of Attorney Act
   1971 of the United Kingdom) must be lodged with this Form for noting. No
   other signatures are acceptable.
 
2. IF YOU HAVE SOLD OR TRANSFERRED ALL YOUR ARAN SHARES

   You should at once send this Form, together with the accompanying Final
   Offer Document and (where provided) the reply-paid envelope, as soon as
   possible to the purchaser or transferee, or, to the bank, stockbroker or
   other agent through whom the sale or transfer was effected for onward
   transmission to the purchaser or transferee. However, this Form of
   Acceptance should not be distributed, forwarded or transmitted to
   Australia, Canada or Japan.
 
3. IF THE SOLE HOLDER HAS DIED

   If the Grant of Probate or Letters of Administration or equivalent
   documentation has/have been registered with Aran (or its registrars), this
   Form must be signed by the personal representative(s) of the deceased or
   equivalent person and lodged with AIB Bank, The Royal Bank of Scotland plc
   or First Chicago Trust Company of New York (as appropriate), at the
   appropriate address given on page 1 of this Form. If the Grant of Probate
   or Letters of Administration or equivalent document has/have not been
   registered with Aran (or its registrars), the personal representative(s) or
   the prospective personal representative(s) should sign this Form in the
   presence of a witness and forward it to AIB Bank, The Royal Bank of
   Scotland plc or First Chicago Trust Company of New York (as appropriate),
   with the share certificate(s) and/or other document(s) of title and a
   sealed copy of the Grant of Probate or Letters of Administration or
   equivalent documentation must be lodged as soon as possible thereafter and
   in any case before the cash remittances due under the Final Offer can be
   forwarded to the personal representative(s).
 
4. IF ONE OF THE HOLDERS OF A JOINT ACCOUNT HAS DIED

   This Form must be signed by all the surviving holders, each in the presence
   of a witness, and lodged with AIB Bank, The Royal Bank of Scotland plc or
   First Chicago Trust Company of New York (as appropriate), at the
   appropriate address given on page 1 of this Form with the share
   certificate(s) and/or other document(s) of title, accompanied by the death
   certificate, Grant of Probate or Letters of Administration or equivalent
   documentation in respect of the deceased holder.
 
5. IF YOU DO NOT HAVE YOUR SHARE CERTIFICATE(S) AND/OR OTHER DOCUMENT(S) OF
   TITLE

   If your share certificate and/or other document(s) of title is/are held by
   your bank or some other agent, complete this Form and, if the share
   certificate(s) is/are readily obtainable, deliver this completed Form to
   your agent for lodging with AIB Bank, The Royal Bank of Scotland plc or
   First Chicago Trust Company of New York (as appropriate), at the
   appropriate address given on page 1 of this Form, accompanied by the share
   certificate(s) and/or other document(s) of title.

   If the share certificate(s) and/or other document(s) of title is/are not
   readily available, you should complete this Form and lodge it together with
   such document(s) of title as is/are available and a letter stating that
   all/the balance of such document(s) of title will follow as soon as
   possible thereafter or alternatively that you have lost one or more of your
   share certificate(s) and, if applicable, arrange for the share
   certificate(s) and/or other document(s) of title to be forwarded as soon as
   possible thereafter.

   If the share certificate(s) and/or other document(s) of title has/have been
   lost, you should complete this Form and lodge it, together with any
   certificate(s) available, with AIB Bank, The Royal Bank of Scotland plc or
   First Chicago Trust Company of New York (as appropriate), at the
   appropriate address given on page 1 of this Form. At the same time you
   should write to the registrars of Aran who are Bank of Ireland, Registrars'
   Department, P.O. Box 4044, Hume House, Ballsbridge, Dublin 4, Ireland,
   advising them of the loss and asking for a letter of indemnity which must
   be completed in accordance with the instructions given. When completed, the
   letter of indemnity must be lodged with AIB Bank, The Royal Bank of
   Scotland plc or First Chicago Trust Company of New York (as appropriate),
   at the address given on page 1 of this Form and to which you sent your Form
   of Acceptance.
 
6. IF THE FORM HAS BEEN SIGNED UNDER POWER OF ATTORNEY

   The completed Form together with the share certificate(s) should be lodged
   with AIB Bank, The Royal Bank of Scotland plc or First Chicago Trust
   Company of New York (as appropriate), at the appropriate address given on
   page 1 of this Form, accompanied by the original power of attorney (or a
   copy thereof duly certified in accordance with the Powers of Attorney Act
   1971 of the United Kingdom) for noting.
  
7. IF YOUR FULL NAME OR OTHER PARTICULARS ARE SHOWN INCORRECTLY ON THE SHARE
   CERTIFICATE(S), FOR EXAMPLE

  (a) Name on the certificate.........................................John Burk
      Correct name...................................................John Burke

      Complete this Form with the correct name and lodge it, accompanied by a
      letter from your bank, stockbroker or solicitor confirming that the
      person described on the certificate(s) and the person who signed this
      Form are one and the same.

  (b) Incorrect address

      Write the correct address on this Form.

  (c) Change of name

  If you have changed your name, lodge your marriage certificate or the deed
  poll with this Form for noting. Cash remittances due to you under the Final
  Offer cannot be sent until all relevant documents have been properly
  completed and lodged, either by post or by hand to AIB Bank, Registrars' &
  New Issue Department, Bankcentre, P.O. Box 954, Ballsbridge, Dublin 4 or
  The Royal Bank of Scotland plc, Registrar's Department, New Issues Section,
  P.O. Box 859, Consort House, East Street, Bedminster, Bristol BS99 1XZ or
  by hand only to The Royal Bank of Scotland plc, Registrar's Department, New
  Issues Section, 67 Lombard Street, London, EC3P 3DL or, if more convenient,
  by post to First Chicago Trust Company of New York, Suite 4660, P.O. Box
  2559, Jersey City, NJ 07303 or by hand or overnight courier to First
  Chicago Trust Company of New York, Suite 4680, 14 Wall Street, Eighth
  Floor, New York, NY 10005. Subject to the provisions of the City Code, ARCO
  Irish Holdings and Rothschilds reserve the right to treat as valid, in
  whole or in part, acceptances of the Final Offer which are not entirely in
  order or which are not accompanied by the relevant share certificate(s)
  and/or other document(s) of title.
 
                   Printed by RR Donnelley Financial, 16384

<PAGE>

                                                                 EXHIBIT (a)(21)

THIS DOCUMENT IS IMPORTANT AND REQUIRES YOUR IMMEDIATE ATTENTION. If you are
in any doubt about any action you should take, you are recommended to seek
advice from your own appropriately authorized independent financial adviser.
 
N M Rothschild & Sons Limited ("Rothschilds") is acting for Atlantic Richfield
Company ("ARCO") and ARCO Irish Holdings Inc. ("ARCO Irish Holdings") in
relation to the Final Offer and no one else, and will not be responsible to
anyone other than ARCO and ARCO Irish Holdings for providing the protection
afforded to customers of Rothschilds nor for providing advice in relation to
the Final Offer. Rothschilds is acting through Rothschild Inc. for the purpose
of making the Final Offer in the United States.
 
If you have sold or otherwise transferred all your American Depositary Shares
("Aran ADSs") of Aran Energy plc ("Aran"), please pass this document and all
accompanying documents as soon as possible to the purchaser or transferee, or
to the bank, stockbroker or other agent through whom the sale or transfer was
effected for transmission to the purchaser or transferee. HOWEVER, SUCH
DOCUMENTS SHOULD NOT BE DISTRIBUTED, FORWARDED OR TRANSMITTED IN OR INTO
AUSTRALIA, CANADA OR JAPAN.
 
This Revised Notice should be read in conjunction with the offer document
dated August 25th, 1995 (the "Original Offer Document") and the accompanying
final offer document dated October 9, 1995 (together with the disclosure
document dated October 9, 1995, the "Final Offer Document"). The definitions
used in the Original Offer Document and Final Offer Document also apply, where
the context requires, in this Revised Notice.
 
- -------------------------------------------------------------------------------
 
                     REVISED NOTICE OF GUARANTEED DELIVERY
 
                                      FOR
 
         ACCEPTANCE OF THE FINAL OFFER FOR AMERICAN DEPOSITARY SHARES
 
                                      OF
 
                                ARAN ENERGY plc
 
          PURSUANT TO THE FINAL OFFER DOCUMENT DATED OCTOBER 9, 1995
 
                                      BY
 
                         N M ROTHSCHILD & SONS LIMITED
 
                                 ON BEHALF OF
 
                           ARCO IRISH HOLDINGS INC.
 
                      (A WHOLLY OWNED SUBSIDIARY OF ARCO)
 
- -------------------------------------------------------------------------------
 
As set forth in "Acceptance Procedures for Holders of Aran ADSs" in Part B of
Appendix 1 to the Original Offer Document, as amended, as applicable, by the
Final Offer Document, this form or one substantially equivalent hereto must be
used for acceptance of the Final Offer in respect of Aran ADSs, if Aran
American Depositary Receipts evidencing Aran ADSs ("Aran ADRs") are not
immediately available or if the procedures for book-entry transfer cannot be
completed on a timely basis or if time will not permit all required documents
to reach the US Depositary prior to the expiration of the Final Offer. Such
form may be delivered by hand or transmitted by facsimile transmission or
mailed to the US Depositary and must include a signature guarantee by an
Eligible Institution in the form set out herein. However, receipt of a Revised
Notice of Guaranteed Delivery or a Notice of Guaranteed Delivery accompanying
the Original Offer Document will not be treated as a valid acceptance for the
purpose of satisfying the Acceptance Condition of the Final Offer. See
"Acceptance Procedures for Holders of Aran ADSs--Guaranteed delivery
procedures" in Part B of Appendix 1 to the Original Offer Document, as
amended, as applicable, by the Final Offer Document.
 
- -------------------------------------------------------------------------------
 
                  TO: FIRST CHICAGO TRUST COMPANY OF NEW YORK
                                 US DEPOSITARY
 
      By Mail:            By Facsimile Transmission         By Hand or Overnight
                      (for Eligible Institutions only):           Delivery:
      
 
     Suite 4660          Fax: (201) 222-4720 or 4721              Suite 4680 
    P.O. Box 2559        Confirm Receipt of Notice of           14 Wall Street
Jersey City, NJ 07303        Guaranteed Delivery                 Eighth Floor
                                by Telephone:                 New York, NY 10005
                               (201) 222-4707          
                        

 
                             For Information call:     
 
                          (800) 659-6111 (Toll Free)
                                      or
                                (201) 324-0137
 
DELIVERY OF THIS INSTRUMENT TO AN ADDRESS, OR TRANSMISSION OF INSTRUCTIONS VIA
A FACSIMILE OR TELEX NUMBER, OTHER THAN AS SET FORTH ABOVE, DOES NOT
CONSTITUTE A VALID DELIVERY.
<PAGE>
 
This form is not to be used to guarantee signatures. If a signature on a
Revised Letter of Transmittal is required to be guaranteed by an Eligible
Institution under the instruction thereto, such signature guarantee must
appear in the applicable space provided in the signature box on the Revised
Letter of Transmittal.
 
ACCEPTANCE OF THE FINAL OFFER IN RESPECT OF ARAN SHARES (EXCEPT INSOFAR AS
THEY ARE REPRESENTED BY ARAN ADSs) MAY NOT BE MADE WITH THIS FORM AND PURSUANT
TO THE GUARANTEED DELIVERY PROCEDURES. IF YOU HOLD ARAN SHARES THAT ARE NOT
REPRESENTED BY ARAN ADSs, YOU CAN OBTAIN A FORM OF ACCEPTANCE FOR ACCEPTING
THE FINAL OFFER IN RESPECT OF THOSE ARAN SHARES FROM THE IRISH RECEIVING
AGENT, THE UK RECEIVING AGENT OR THE US DEPOSITARY. SEE INSTRUCTION 13 OF THE
REVISED LETTER OF TRANSMITTAL.
 
Ladies and Gentlemen:
 
The undersigned hereby accepts the Final Offer in respect of Aran ADSs upon
the terms and subject to the conditions set forth below pursuant to the
guaranteed delivery procedures set out in "Acceptance Procedures for Holders
of Aran ADSs--Guaranteed delivery procedures" in Part B of Appendix 1 to the
Original Offer Document, as amended, as applicable, by the Final Offer
Document.
 
THE UNDERSIGNED UNDERSTANDS THAT THE ACCEPTANCE OF THE FINAL OFFER IN RESPECT
OF ARAN ADSs PURSUANT TO THE GUARANTEED DELIVERY PROCEDURES WILL NOT BE
TREATED AS A VALID ACCEPTANCE FOR THE PURPOSE OF SATISFYING THE ACCEPTANCE
CONDITION. SEE "ACCEPTANCE PROCEDURES FOR HOLDERS OF ARAN ADSs--GUARANTEED
DELIVERY PROCEDURES" IN PART B OF APPENDIX 1 TO THE ORIGINAL OFFER DOCUMENT,
AS AMENDED, AS APPLICABLE, BY THE FINAL OFFER DOCUMENT. TO BE COUNTED TOWARDS
SATISFACTION OF THIS CONDITION, THE ARAN ADRs EVIDENCING SUCH ARAN ADSs MUST
BE RECEIVED BY THE US DEPOSITARY OR, IF APPLICABLE, TIMELY CONFIRMATION OF A
BOOK-ENTRY TRANSFER OF SUCH ARAN ADSs INTO THE US DEPOSITARY'S ACCOUNT AT A
BOOK-ENTRY TRANSFER FACILITY PURSUANT TO THE PROCEDURES SET OUT IN "ACCEPTANCE
PROCEDURES FOR HOLDERS OF ARAN ADSs--BOOK ENTRY TRANSFER FACILITIES" IN PART B
OF APPENDIX 1 TO THE ORIGINAL OFFER DOCUMENT, AS AMENDED, AS APPLICABLE, BY
THE FINAL OFFER DOCUMENT, MUST BE RECEIVED BY THE US DEPOSITARY, TOGETHER WITH
A DULY EXECUTED REVISED LETTER OF TRANSMITTAL OR LETTER OF TRANSMITTAL
ACCOMPANYING THE ORIGINAL OFFER DOCUMENT (OR FACSIMILE THEREOF) WITH ANY
REQUIRED SIGNATURE GUARANTEES AND ANY OTHER REQUIRED DOCUMENTS.
 
Number of Aran ADSs: ________________    Name of Record Holder(s): ___________
 
Aran ADR No.(s) (if available): _____    _____________________________________
 
_____________________________________    _____________________________________
                                                (Please type or print)
 
_____________________________________    Address: ____________________________
 
If Aran ADSs will be tendered by         _____________________________________
book-entry transfer, check one box:
 
                                         Area Code and Tel. No.: _____________
[_] The Depositary Trust Company
                                         Signature(s): _______________________
[_] Midwest Securities Trust Company
                                         _____________________________________
[_] Philadelphia Depositary Trust
    Company
                                         _____________________________________
 
Account Number: _____________________    Dated: ______________________________
<PAGE>
 
                                   GUARANTEE
                   (NOT TO BE USED FOR SIGNATURE GUARANTEES)
 
  The undersigned, a participant in the Securities Transfer Agents Medallion
Program, the New York Stock Exchange Medallion Program or the Stock Exchanges
Medallion Program, hereby guarantees that the undersigned will deliver to the
US Depositary either the Aran ADRs representing the Aran ADSs with respect to
which the Final Offer is being accepted hereby, in proper form for transfer,
or confirmation of the book-entry transfer of such Aran ADSs into the US
Depositary's account at The Depositary Trust Company, the Midwest Securities
Trust Company or the Philadelphia Depositary Trust Company, in any such case
together with a properly completed and duly executed Revised Letter of
Transmittal or Letter of Transmittal accompanying the Original Offer Document
(or manually signed facsimiles thereof), with any required signature
guarantees and any other required documents, all within three NASDAQ trading
days after the date hereof.
 
  The Eligible Institution that completes this form must communicate the
guarantee to the US Depositary and must deliver the Revised Letter of
Transmittal or the Letter of Transmittal accompanying the Original Offer
Document and Aran ADRs to the US Depositary within the time periods shown
herein. Failure to do so could result in a financial loss to such Eligible
Institution.
 
Number of Firm, Agent or Trustee: ___    _____________________________________
                                                (Authorized Signature)
 
_____________________________________    Name: _______________________________
                                                (Please type or print)
 
Address: ____________________________    Title: ______________________________
                           (Zip Code)
 
Area Code and Tel. No.: _____________    Dated: ______________________________
 
NOTE: DO NOT SEND ARAN ADRs WITH THIS FORM; ARAN ADRs SHOULD BE SENT WITH YOUR
      REVISED LETTER OF TRANSMITTAL OR THE LETTER OF TRANSMITTAL ACCOMPANYING
      THE ORIGINAL OFFER DOCUMENT

<PAGE>
 
                                                                 EXHIBIT (a)(22)

THIS DOCUMENT IS IMPORTANT AND REQUIRES YOUR IMMEDIATE ATTENTION. If you are
in any doubt as to the nature of the proposal or what action to take, you are
recommended to seek your own personal advice from your stockbroker, bank
manager, solicitor, accountant or other independent professional adviser
immediately.
 
If you have sold or otherwise transferred all your shares in Aran Energy plc,
please pass this document as soon as possible to the purchaser or transferee,
or to the bank, stockbroker or other agent through whom the sale or transfer
was effected, for onward transmission to the purchaser or transferee. HOWEVER,
THIS DOCUMENT SHOULD NOT BE FORWARDED OR TRANSMITTED IN OR INTO AUSTRALIA,
CANADA OR JAPAN.
 
N M Rothschild & Sons Limited ("Rothschilds") is acting for Atlantic Richfield
Company ("ARCO") and ARCO Irish Holdings Inc. ("ARCO Irish Holdings") in
connection with the Final Offer and no one else, and will not be responsible
to anyone other than ARCO and ARCO Irish Holdings for providing the protection
afforded to customers of Rothschilds or for providing advice in relation to
the Final Offer. Rothschilds is acting through Rothschild Inc. for the purpose
of making the Final Offer in the United States.
 
- -------------------------------------------------------------------------------
 
                           ARCO IRISH HOLDINGS [LOGO]
 
                               FINAL CASH OFFER
 
                                      FOR
 
                                ARAN ENERGY plc
 
 
                                 FORM OF PROXY
 
                      FOR USE IN CONNECTION WITH THE ARAN
      EXTRAORDINARY GENERAL MEETING CONVENED FOR 23 OCTOBER 1995 ("EGM")
 
- -------------------------------------------------------------------------------
 
The price under the Final Offer will be IR68p per Aran share only if the
Connemara proposal is voted down. You are urged to vote against the resolution
to be proposed at the EGM and to complete and despatch the Form of Proxy,
following the instructions overleaf. TO ENABLE THE FORM OF THE PROXY TO BE
VALIDLY LODGED IN ACCORDANCE WITH THE ARTICLES OF ASSOCIATION OF ARAN, YOU
SHOULD COMPLETE AND DESPATCH THE FORM AS SOON AS POSSIBLE AND IN ANY EVENT TO
BE RECEIVED ON OR BEFORE THE CLOSE OF BUSINESS ON 20 OCTOBER 1995.
 
Completion of the Form of Proxy in accordance with the instructions overleaf
will appoint any Director of N M Rothschild & Sons Limited as your proxy to
vote AGAINST the resolution. Whether or not you complete a Form of Proxy
and/or vote at the EGM you are entitled to, and urged to, accept the Final
Offer.
 
Completion and return of the Form of Proxy will not preclude you from
attending and voting at the EGM.
 
This document should be read in conjunction with the Final Offer Document with
which it is enclosed. Terms defined in the Final Offer document have the same
meaning in this document. The Directors of ARCO Irish Holdings and the members
of the bid committee of ARCO accept responsibility for the information
contained in this document. To the best of the knowledge and belief of the
directors of ARCO Irish Holdings and the bid committee of ARCO (who have taken
all reasonable care to ensure that such is the case) the information contained
in this document is in accordance with the facts and does not omit anything
likely to affect the import of such information.
<PAGE>
 
INSTRUCTIONS ON COMPLETING FORM OF PROXY TO VOTE AGAINST RESOLUTION
 
 
1. INSERT NAME OF REGISTERED HOLDER OF SHARES                            [ARROW]
 
2. INSERT ADDRESS OF REGISTERED                                          [ARROW]
   HOLDER OF SHARES
                                                                         
3. DELETE "THE CHAIRMAN OF THE MEETING"                                  [ARROW]
 
4. INSERT "ANY DIRECTOR OF N M ROTHSCHILD & SONS LIMITED"                [ARROW]
 
5. INSERT "NEW COURT, ST. SWITHIN'S LANE, LONDON EC4P 4DU"               [ARROW]
 


6. INSERT X IN BOX MARKED "AGAINST"                                      [ARROW]

 
                                                                               
7. INSERT DATE HERE                                                      [ARROW]
 
8. SIGN HERE                                                             [ARROW]
 
IMPORTANT: YOU SHOULD ALSO FOLLOW CAREFULLY THE NOTES AT THE FOOT OF THE FORM OF
           PROXY

WHEN YOU HAVE COMPLETED THE FORM, PLEASE DESPATCH IT IMMEDIATELY -- IGNORE THE
ADDRESS IN NOTE 1 FOR THESE PURPOSES
<PAGE>
 
                                ARAN ENERGY PLC
 
                                 FORM OF PROXY
 
For use at the Extraordinary General Meeting to be held on 23 October 1995 and
at any adjournment thereof.
 
I/We ...........................................................................
                                (BLOCK LETTERS)
of .............................................................................
 
being a member/members of the above-named Company hereby appoint the Chairman
of the Meeting+
 ................................................................................

of .............................................................................
 
as my/our proxy to vote for me/us on my/our behalf at the Extraordinary General
Meeting of the Company to be held on 23 October 1995 and at any adjournment
thereof. I/We direct that my/our vote(s) be cast on the Resolution below as
indicated by an X in the appropriate box:
 
RESOLUTION                
To approve the farm-out of an                 FOR*           AGAINST* 
aggregate 47.5 per cent. interest             [_]              [_]     
in the Connemara Lease Undertaking
by Aran Servicing Limited to Statoil
(U.K.) Limited.
 
+ If it is desired to appoint another person as a proxy the words "the Chairman
of the Meeting" should be deleted and the name and address of the proxy, who
need not be a member of the Company, inserted.
 
* Unless otherwise directed, and in respect of any other resolution properly
moved at the Meeting, the proxy will vote, or may abstain from voting, as he
thinks fit.
 
Dated this ....... day of ...... 1995
 

Signature ......................................................................
 
NOTES
1. To be valid the Form of Proxy duly signed, together with the power of
   attorney or other authority (if any) under which it is signed (or a
   notarially certified copy thereof), must be deposited at the Company's
   Registrars, Bank of Ireland, Registration Department, P.O. Box 4044, Fourth
   Floor, Hume House, Ballsbridge, Dublin 4, not less than forty-eight hours
   before the time appointed for the Meeting or any adjournment thereof at
   which the person named in the Form is to vote.
2. If the Form of Proxy is given by a body corporate, it must be given under
   its Common Seal or under the hand of an attorney or officer duly authorised.
3. A proxy need not be a member of the Company.
4. In the case of joint holders the vote of the senior who tenders a vote,
   whether in person or by proxy, shall be accepted to the exclusion of the
   votes of the other joint holders and for this purpose seniority shall be
   determined by the order in which the names stand in the Register of Members
   in respect of the joint holding.
5. Completion and return of the Form of Proxy will not preclude shareholders
   from attending and voting at the Meeting.

<PAGE>

                                                                 EXHIBIT (a)(23)

This announcement is neither an offer to purchase nor a solicitation of an
offer to purchase securities. The Final Offer is made in the United States
solely by the Final Offer Document dated October 9, 1995 (together with the
disclosure document dated October 9, 1995), the Original Offer Document dated
August 25, 1995 and the related Acceptance Forms (which collectively constitute
the Final Offer) and is not being made to, nor will the Final Offer be accepted
from or on behalf of, holders of Aran Ordinary Shares or Aran ADSs in any
jurisdiction in which the making or acceptance thereof would not be in
compliance with the laws of such jurisdictions. In those jurisdictions whose
securities laws or blue sky laws require the Final Offer to be made by a
licensed broker or dealer, the Final Offer shall be deemed to be made on behalf
of ARCO Irish Holdings Inc. by Rothschild Inc. or one or more registered
brokers or dealers which are licensed under the laws of those jurisdictions.
The Final Offer Document, the disclosure document dated October 9, 1995, the
Original Offer Document, the Acceptance Forms and related materials should not
be forwarded or transmitted in or into Australia, Canada or Japan.

                               FINAL CASH OFFER

                                      BY

                         N M ROTHSCHILD & SONS LIMITED

                                 ON BEHALF OF

                           ARCO IRISH HOLDINGS INC.

                         A WHOLLY OWNED SUBSIDIARY OF

                          ATLANTIC RICHFIELD COMPANY

                          TO ACQUIRE ALL OUTSTANDING

                ORDINARY SHARES AND AMERICAN DEPOSITARY SHARES

                                      OF

                                ARAN ENERGY PLC

     N M Rothschild & Sons Limited, acting in the United States through
Rothschild Inc., on behalf of ARCO Irish Holdings Inc. ("ARCO Irish Holdings"),
a wholly owned subsidiary of Atlantic Richfield Company ("ARCO"), is offering to
purchase the entire issued (and to be issued) share capital of Aran Energy plc
("Aran"), upon the terms and subject to the conditions set forth in the Offer
Document dated August 25, 1995 (the "Original Offer Document"), the Final Offer
Document dated October 9, 1995 (together with the disclosure document dated
October 9, 1995, the "Final Offer Document") and the related Acceptance Forms on
the following bases:

 . For each Ordinary Share ("Aran Share"):              IR68p in cash 

 . For each American Depositary Share ("Aran ADS")
  which represents 30 Aran Shares:                     IR(POUND) 20.40 in cash 

     In the event that the Statoil/Connemara proposal (being the proposed
farm-out of an aggregate 47.5% interest in the Connemara Lease Undertaking by
Aran Servicing Limited to Statoil (U.K.) Limited ("Statoil")) is approved at
the Extraordinary General Meeting of Aran shareholders convened for October 23,
1995 or at any adjournment thereof (the "Aran Meeting"), the consideration
payable under the Final Offer will instead be as follows:

 . For each Aran Share:                                 IR66p in cash 

 . For each Aran ADS which represents 30 Aran Shares:   IR(POUND) 19.80 in cash 

     ARCO and ARCO Irish Holdings are opposed to the Statoil/Connemara proposal
and believe it transfers value from Aran shareholders to Statoil. Accordingly,
ARCO and ARCO Irish Holdings have structured the Final Offer to meet the
possibility of the Statoil/Connemara proposal being approved and the resulting
diminution in shareholder value.

                     Key Points for Aran's Securityholders

 . The Final Offer will be open for acceptance until 1:00 p.m. (Dublin and London
  time), 9:00 a.m. (New York City time), on October 24, 1995. It will not be
  extended, nor will it be revised or increased, except that ARCO Irish Holdings
  reserves the right to increase, extend or otherwise revise the Final Offer
  should the U.K. Panel on Takeovers and Mergers (the "U.K. Panel") so agree or
  in the event of a competitive situation (including an offer or an intention to
  make an offer being announced by or on behalf of the unnamed third party
  referred to in Aran's announcement of October 6, 1995) arising (as determined
  by the U.K. Panel).

 . The Final Offer is conditioned, among other things, on valid acceptances being
  received in respect of not less than 95% of the Aran Shares (including Aran
  Shares represented by Aran ADSs) to which the Final Offer relates, or such
  lesser percentage as ARCO Irish Holdings may decide (the "acceptance level"),
  provided that such condition (the "Acceptance Condition") shall not be
  satisfied unless ARCO Irish Holdings and/or its wholly owned subsidiaries
  shall have acquired or agreed to acquire, pursuant to the Final Offer or
  otherwise, Aran Shares (including Aran Shares represented by Aran ADSs)
  carrying more than 50% of the voting rights normally exercisable at general
  meetings of Aran. ARCO Irish Holdings intends to revise the Acceptance
  Condition at the earliest opportunity so that the condition will have been
  satisfied if ARCO Irish Holdings and/or its wholly owned subsidiaries shall
  have acquired or agreed to acquire, pursuant to the Final Offer or otherwise,
  Aran Shares (including Aran Shares represented by Aran ADSs) carrying more
  than 50% of the voting rights normally exercisable at general meetings of
  Aran, including, for this purpose, any such voting rights attaching (or which
  on issue will attach) to any Aran Shares (including Aran Shares represented by
  Aran ADSs) which have been unconditionally allotted or issued before the
  Acceptance Condition (as reduced) is satisfied whether pursuant to the
  exercise of any outstanding subscription or conversion rights or otherwise.
  Accordingly, subject to ARCO Irish Holdings not being aware of any
  circumstance which constitutes or may result in a breach of or failure to
  satisfy any of the remaining conditions to the Final Offer (other than
  condition (a), the Acceptance Condition, and condition (b) relating to the
  granting of Irish Mergers Act clearance), ARCO Irish Holdings intends on
  October 19, 1995 to give three U.S. Business Days' notice to reduce the
  acceptance level as described above with effect on and from October 24, 1995.
  
 . Holders of Aran Shares who wish to accept the Final Offer should use the 
  Revised Form of Acceptance. The Revised Form of Acceptance permits a tendering
  holder of Aran Shares to elect, by completing the appropriate box(es), either
  (i) to accept the Final Offer in respect of all or some of such holder's Aran
  Shares at the applicable price determined as described above, (ii) to accept
  the Final Offer only if the Statoil/Connemara proposal is voted down by the
  Aran shareholders at the Aran Meeting (i.e., only at the higher price) or only
  if the Statoil/Connemara proposal is approved (i.e., only at the lower price)
  or (iii) to accept the Final Offer in relation to a different number of Aran
  Shares depending on whether the Statoil/Connemara proposal is or is not
  approved by the Aran shareholders at the Aran Meeting. Copies of the Revised
  Form of Acceptance are available from the U.S. Depositary at the addresses and
  telephone numbers set forth below.

 . Holders of Aran ADSs who wish to accept the Final Offer should use (i) either
  the Revised Letter of Transmittal or the Letter of Transmittal accompanying
  the Original Offer Document and (ii) if such tendering holder wishes to
  utilize the guaranteed delivery procedures set forth in the Final Offer,
  either the Revised Notice of Guaranteed Delivery or the Notice of Guaranteed
  Delivery accompanying the Original Offer Document. Tenders of Aran ADSs
  pursuant to the Letter of Transmittal accompanying the Original Offer Document
  shall be deemed to constitute an acceptance of the Final Offer in respect of
  all such Aran ADSs at the applicable price determined as described above. The
  Revised Letter of Transmittal permits a tendering holder of Aran ADSs to
  elect, by completing the appropriate box(es), either (i) to accept the Final
  Offer in respect of all or some of such holder's Aran ADSs at the applicable
  price determined as described above, (ii) to accept the Final Offer only if
  the Statoil/Connemara proposal is voted down by the Aran shareholders at the
  Aran Meeting (i.e., only at the higher price) or only if the Statoil/Connemara
  proposal is approved (i.e., only at the lower price) or (iii) to accept the
  Final Offer in relation to a different number of Aran ADSs depending on
  whether the Statoil/Connemara proposal is or is not approved by the Aran
  shareholders at the Aran Meeting. Copies of the Revised Letter of Transmittal
  and the Revised Notice of Guaranteed Delivery are available from the U.S.
  Depositary at the addresses and telephone numbers set forth below.

 . There can be no assurance that the results of the Aran Meeting will be
  available prior to the termination of withdrawal rights. Accordingly, we urge
  you to consider carefully the elections you can make regarding the
  Statoil/Connemara proposal in the Revised Form of Acceptance and the Revised
  Letter of Transmittal. Please note that if you submit a duly executed Revised
  Form of Acceptance or Revised Letter of Transmittal and fail to make any
  election regarding the basis on which you are accepting the Final Offer, you
  will be deemed to have accepted the Final Offer in respect of all Aran Shares
  or Aran ADSs tendered thereby at the applicable price determined as described
  above.

 . Withdrawals of previous tenders of Aran ADSs pursuant to Letters of
  Transmittal may be made in writing or by facsimile transmission to the U.S.
  Depositary at the addresses and facsimile copy number set forth below in
  accordance with the procedures set forth in the Final Offer Document and the
  Original Offer Document. Aran ADS holders may submit such facsimile
  withdrawals 24 hours a day, up to 9:00 a.m. (New York City time) on October
  24, 1995. Delivery of a properly completed and duly executed Revised Letter of
  Transmittal in accordance with the procedures set forth in the Final Offer
  Document and the Original Offer Document will automatically constitute a
  revocation of any Letter of Transmittal previously delivered by the tendering
  Aran ADS holder.

 . Aran securityholders may telephone the U.S. Depositary at (800) 659-6111 (Toll
  Free 24 Hours) in order to obtain the results of the Aran Meeting (when
  disclosed by Aran).

 . Completion of the acceptance procedures will take longer than you expect.
  Don't wait for the last moment! 

     Requests for assistance or copies of the Final Offer Document, the Original
Offer Document, the circular from ARCO Irish Holdings to Aran securityholders
dated September 14, 1995, the Revised Form of Acceptance, the Revised Letter of
Transmittal and the Revised Notice of Guaranteed Delivery may be directed to
the U.S. Depositary at the addresses and telephone numbers set forth below, and
copies will be furnished promptly at ARCO Irish Holdings' expense.

                  The U.S. Depositary for the Final Offer is:

                    FIRST CHICAGO TRUST COMPANY OF NEW YORK
                                  Suite 4680
                                14 Wall Street
                                 Eighth Floor
                           New York, New York 10005
     Facsimile Copy Number:                      For Information Call:

     (201) 222-4720 or 4721                   (800) 659-6111 (Toll Free)
      Confirm by Telephone:                       or (201) 324-0137
         (201) 422-4707  


           By Mail:                          By Hand or Overnight Courier:
 
          Suite 4660                                  Suite 4680
        P.O. Box 2559                               14 Wall Street
 Jersey City, New Jersey 07303                       Eighth Floor
                                               New York, New York 10005

        The Dealer Manager for the Final Offer in the United States is:

                                ROTHSCHILD INC.
                          1251 Avenue of the Americas
                                  51st Floor
                              New York, NY 10020
                      (212) 403-3611 within New York City
          (800) 753-5151 ext. 3611 (Toll Free) outside New York City

October 10, 1995


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