1 Exhibit 23(c) CONSENT OF SIMMONS & COMPANY INTERNATIONAL Houston, Texas January 15, 1996 We hereby consent to: (i) the inclusion as an Appendix to the Registration Statement related to the merger of a wholly owned subsidiary of Tesoro Petroleum Corporation with Coastwide Energy Services, Inc. ("Coastwide") on form S-4 (the "Tesoro S-4") of our opinion as to the fairness, from a financial point of view, to the holders of shares of Common Stock, Convertible Debentures and Class B Warrants of Coastwide of the consideration to be received by such holders; and (ii) the use of certain information from such opinion in the Tesoro S-4. SIMMONS & COMPANY INTERNATIONAL /s/ NICHOLAS L. SWYKA - ------------------------ Nicholas L. Swyka Managing Director