It was first known as Sigmor, then Sigmor Shamrock, some years later as Diamond Shamrock and finally as Valero. TETCO came in sometime during a spinoff I think.
In the beginning they where cheaper than other outlets. The stations were very barebones, with nothing but a small cashier area, restrooms and vending machines for snacks. They were only there to sell gas and oil with not servicing area.
I remember it first being a cash only business. When they started taking credit cards, they would take any other companies card, imprint it and write in your address from your driver’s license.
I remember this company having gas stations around the Central Texas. The one I remember the best was on US 281 just north of the airport in San Antonio. (where Wuzbach Parkway crosses now) We always stopped there, either going to San Antonio from Marble Falls or as we left heading back home. It was by far the cheapest gas all up and down the highway.
Sometime in the 70’s I got crosswise with them because some of our employees had company gas cards and when they filled up, they would send the bill to that employees home address. It became mass confusion trying to get all that verified and straightened out.
The Sigmor Story from Wikipedia
During the 1930s and 1940s Sigfried (Sig) Moore operated the chain. In 1943 Moore loaned Thomas E. Turner, an employee, money to launch his own business. Turner decided to use the name Sigmor for the chain of stores he established during the 40s and 50s. In 1952 Sigmor was incorporated. In 1959 a restructuring took place which allowed each separate gas station to incorporate separately. In 1960 most of the chain was purchased by Shamrock and then leased back to Turner, who continued to lead the company. In 1978 Sigmor purchased its stations back from Diamond Shamrock, continuing to market DS products. By 1983 Sigmor was one of the largest independent service-station chains in the USA. The merger gave Diamond Shamrock 600 retail outlets, plus the Three Rivers oil refinery which was built by Sigmor during the 1970s. In 1987 The Diamond Shamrock Refining and Marketing Company severed ties with Diamond Shamrock Corporation, which was the parent company, and became independent with its headquarters in San Antonio. At that time, as part of the reorganization, Diamond Shamrock Corporation became Maxus Energy Corporation, severing all legal ties to the Diamond Shamrock Refining and Marketing Company. In 1990 Diamond Shamrock Refining and Marketing Company shortened its name to Diamond Shamrock, Incorporated, as it had taken the step of incorporating at that time.