<PAGE>
Exhibit 11
Tetra Tech, Inc.
Computation of Net Income Per Common Share
(Unaudited)
<TABLE>
<CAPTION>
THREE MONTHS ENDED NINE MONTHS ENDED
--------------------------------- ---------------------------------
July 2, July 4, July 2, July 4,
2000 1999 2000 1999
--------------- ---------------- --------------- ----------------
<S> <C> <C> <C> <C>
Basic:
Common stock outstanding, beginning
of period............................ 38,663,000 37,578,000 38,434,000 35,788,000
Exchanged stock........................ -- 6,000 -- 143,000
Stock options exercised................ 201,000 73,000 418,000 244,000
Stock purchase plan issuance........... 166,000 156,000 166,000 156,000
Issuance of common stock............... 573,000 364,000 585,000 1,846,000
Payment of fractional shares........... -- (45,000) -- (45,000)
-------------- --------------- --------------- ----------------
Common stock outstanding, end
of period............................ 39,603,000 38,132,000 39,603,000 38,132,000
============== =============== =============== ================
Weighted average common stock
outstanding during the period........ 39,287,000 37,801,000 38,768,000 36,805,000
============== =============== =============== ================
Net income as reported in condensed
consolidated financial statements.... $ 9,920,000 $ 8,503,000 $ 25,608,000 $ 20,392,000
============== ============== =============== ================
Basic Earnings Per Share............... $ 0.25 $ 0.22 $ 0.66 $ 0.55
============== ============== =============== ================
Diluted:
Weighted average common stock
outstanding during the period........ 39,287,000 37,801,000 38,768,000 36,805,000
Potential common shares under the
treasury stock method assuming the
exercise of options and warrants
and the conversion of preferred
stock and exchangeable stock of a
subsidiary........................... 2,817,000 2,344,000 2,453,000 2,461,000
-------------- --------------- --------------- ----------------
Total............................ 42,104,000 40,145,000 41,221,000 39,266,000
============== ============== =============== ================
Net income as reported in condensed
consolidated financial statements.... $ 9,920,000 $ 8,503,000 $ 25,608,000 $ 20,392,000
============== ============== =============== ================
Diluted Earnings Per Share............. $ 0.24 $ 0.21 $ 0.62 $ 0.52
============== ============== =============== ================
</TABLE>
See accompanying Notes to the Condensed Consolidated Financial Statements.
