Marathon Petroleum Corp. said on April 30 it would buy rival Andeavor for more than $23 billion to form a company that would leapfrog Valero Energy Corp as the largest U.S. refiner by capacity.

The cash-and-stock deal values Andeavor at about $152 per share, representing a premium of about 24% to Andeavor stock's close on April 27.

The combined company will have the ability to process about 3.1 million barrels per day and have a large network of retail stations, oil, natural gas and refined products pipelines.

The deal is expected to produce $1 billion of synergies, Marathon said.

Marathon Chief Executive Gary Heminger will run the combined company, with a senior role for Andeavor's chief executive, Gregory Goff.

San Antonio, Texas-based Andeavor, formerly known as Tesoro, operates 10 refineries in the western United States with a refining capacity of about 1.2 million barrels per day, and ownership in a logistics business, according to Andeavor website.

Valero, which has similar overall refining capacity of 3.1 million barrels per day, has refineries in Canada and Britain apart from the United States.