Marathon Petroleum is one of the largest oil refiners in the United States, converting crude oil into gasoline, diesel and other fuels, and also operates a large network of pipelines and storage terminals through its ownership stake in MPLX, a separately traded midstream partnership. As a refiner, its profitability depends heavily on the crack spread, the gap between what it pays for crude oil and what it can sell refined products for, rather than the price of oil itself. The company also runs a retail fuel and convenience store business under the Marathon and other brands, giving it a direct-to-consumer outlet for some of the fuel it refines. Refining margins can swing significantly with seasonal driving demand, refinery maintenance schedules and shifts in fuel export markets, making Marathon's quarterly results considerably more volatile than a typical industrial company's.