Valero has purchased the refinery for $730m, excluding working capital, and was funded from available cash.
The company said the Welsh unit is the largest and most complex refineries in Europe and has total capacity of 270,000 barrels per day.
The company now has 15 refineries, with a combined capacity of 2.9 million barrels of throughput.
Valero President for Europe Joe Gorder said this acquisition fits perfectly, and the company has acquired one of the finest refining, marketing and logistics operations in all Europe.
