Exhibit 16.1 April 4, 1997 Securities and Exchange Commission 450 Fifth Street, N.W. Washington, D.C. 20549 Ladies and Gentlemen: We have read Item 4 of Ultramar Diamond Shamrock Corporation's Form 8-K/A dated March 4, 1997 and filed with the Securities and Exchange Commission on April 4, 1997, and are in agreement with the statements contained in paragraph 4(a) therein as they relate to Price Waterhouse LLP. Yours very truly, /s/ PRICE WATERHOUSE LLP PRICE WATERHOUSE LLP W5077.TW