Also known as:
Diamond Shamrock was an independent refiner operating in the US.
The company ultimately Merged with Ultramar to form Ultramar Diamond Shamrock (UDS).
1967 - Shamrock and Diamond merged to form Diamond Shamrock
1984 - Diamond Shamrock acquired Three Rivers refinery from Sigmor
1997 - Ultramar and Diamond Shamrock merged to form Ultramar Diamond Shamrock