Marathon Petroleum's purchase of Andeavor stands to capitalize on some of the biggest trends in the energy industry. : A planned merger to form the nation's biggest independent oil refiner stands to capitalize on some of the biggest trends in the energy industry. Marathon Petroleum's proposed $23 billion purchase of Andeavor would make the combined company one of the biggest operators of U.S. gas station convenience stores. It would also assemble a portfolio of refining assets that stretches from the West Coast to the Midwest at a time when profit margins for refiners are booming.