Federal antitrust regulators have cleared the sale of Shell Oil Co.’s Wilmington refinery and 250 Southern California retail gas locations to San Antonio-based independent oil company Tesoro Corp.

The government has completed its investigation of the sale and the mandatory waiting period on the transaction has expired, according to a notice issued Thursday by the Federal Trade Commission.

Tesoro Corp.’s $1.6 billion purchase of the oil refinery and retail gas stations will bring a new player into the California market, but it will have a minimal impact on gas prices, experts said.

Tesoro also bought an additional 140 USA-branded California stations in a separate $277 million deal. The acquisitions give Tesoro about 4.2 percent of the state’s retail gas market.