Marathon Petroleum's Business In-Depth With that in mind, let's take a look at Marathon Petroleum's main business drivers. Findlay, OH-based Marathon Petroleum Corporation is a leading independent refiner, transporter and marketer of petroleum products. The company, in its current form, came into existence following the 2011 spin-off of Houston, TX-based Marathon Oil Corporation's refining/sales business into a separate, independent and publicly-traded entity. In October 2018, Marathon Oil completed the acquisition of its rival Andeavor in a $23.3 billion deal, thereby becoming the nationwide largest refining company by market capitalization.