"Diamond Shamrock Corp. or Diamond Shamrock Refining and Marketing was an oil refinery and gas station company in the United States, headquartered in San Antonio, Texas.
Since ...
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2001, it operates as a brand of Valero and has withdrawn the brand from a majority of Texas gas stations and had converted most of the stores to Valero or sold them off to Texaco or other companies." - (en.wikipedia.org 29.01.2020)