According to Statista, the five biggest oil refining companies by capacity in 2023 were:Sinopec (China): 5.2 million barrels per day (bpd) of capacity.ExxonMobil (U.S.): 4.5 million bpd.Saudi Aramco (Saudi Arabia): 4.1 million bpd.Valero (U.S.): 3.2 million bpd.Marathon Petroleum (U.S.): 3.0 million bpd.

Marathon Petroleum built the last major U.S. refinery in 1977. It still operates the Garyville, La., facility, which it has expanded from its initial capacity of 200,000 bpd to its current capacity of 597,000 bpd.However, several companies have built refinery expansions over the years. The most recent was ExxonMobil's Beaumont, Texas, refinery, which expanded in 2023 to 609,024 bpd, making it the country's third-largest refinery. Meanwhile, Motiva upgraded its Port Arthur, Texas, refinery in 2012 to 626,000 bpd, making it the country's second-largest facility.

There are many excellent oil stock investments. Some of the best oil stocks to buy are ConocoPhillips (NYSE: COP), Devon Energy (NYSE: DVN, Enbridge (NYSE: ENB), ExxonMobil (NYSE: XOM), and Phillips 66 (NYSE: PSX). They have large, diversified, and low-cost operations and strong balance sheets, which help them weather the sector's volatility better than others.