Jones Day and Sullivan & Cromwell are advising on a $23.3 billion energy deal that, when completed, will create the nation’s largest refiner.

Marathon Petroleum Corp., represented by Jones Day, and San Antonio-based Andeavor, formerly Tesoro Corp., advised by Sullivan & Cromwell, announced on Monday they have reached a definitive merger agreement in which Marathon will acquire all outstanding Andeavor shares for a total of $23.3 billion. Andeavor shareholders can choose to take 1.87 shares of Marathon stock or $152.77 in cash for their Andeavor shares.