<PAGE>
 
The Board of Directors
Zapata Corporation
September 20, 1995
Page 2


Schroder Wertheim, as part of its investment banking business, is continually 
engaged in the valuation of businesses and their securities in connection with 
mergers and acquisitions, negotiated underwritings, secondary distributions of 
listed and unlisted securities, private placements and valuations for estate, 
corporate and other purposes. Schroder Wertheim is a full service securities 
firm and in the course of our normal trading activities we may from time to time
effect transactions and hold positions in securities of Zapata and Enterra.
Schroder Wertheim acted as financial advisor to Zapata regarding the Company's 
negotiations with Enterra and will receive a fee which is contingent upon 
consummation of the Transaction. Schroder Wertheim rendered investment banking 
services to Zapata in another transaction for which the firm received a 
customary fee and has also been engaged as Zapata's financial advisor to assist 
in the potential divestiture of Zapata's wholly owned subsidiary, Cimaron Gas 
Holding Company, and its subsidiaries.

In connection with the Opinion set forth herein, we have, among other things:

(i)    reviewed the Draft Purchase Agreement and the Glazer Letter;

(ii)   reviewed the unaudited financial statements of EI for the (i) twelve 
       months ended December 31, 1992, (ii) ten months ended October 31, 1993,
       (iii) eleven months ended September 30, 1994, (iv) eight months ended May
       31, 1995, (v) eleven months ended August 31, 1995, all of which were
       prepared by Zapata management;

(iii)  reviewed the pro forma unaudited financial statements of EI for the (i) 
       twelve months ended October 31, 1993, (ii) twelve months ended September
       30, 1994, (iii) eight months ended May 31, 1994, and (iv) eleven months
       ended August 31, 1994, all of which were prepared by Zapata management;

(iv)   reviewed and discussed, with the management of Zapata and EI, certain 
       financial information prepared by management, including the historical
       pro forma financial results referred to above, and EI management's
       projections for future periods, as well as the current financial
       condition and business prospects of EI;

(v)    compared certain financial data for EI under the proposed terms of the 
       Transaction with that of certain publicly traded companies which we
       deemed to be reasonably comparable to EI;

(vi)   compared the financial terms, to the extent publicly available, of 
       certain recent acquisition transactions which we deemed to be reasonably
       comparable to the proposed financial terms of the Transaction;

(vii)  actively solicited the interest of potential buyers, held discussions, 
       both in person and via telephone, with potential buyers regarding their
       interest in acquiring EI, and reviewed written acquisition proposals
       relating to EI;

(viii) visited EI's facilities in Corpus Christi, Texas; and

(ix)   performed such other financial studies, analyses, inquiries and 
       investigations as we deemed appropriate.