Leading Oil And Gas Companies In The US

The American oil and gas business runs on a handful of giants, and the lineup has been reshuffled hard in the past few years by a wave of mega-deals. ExxonMobil swallowed Pioneer Natural Resources, Chevron closed a long fight to buy Hess, and ConocoPhillips absorbed Marathon Oil, so several names that used to anchor these rankings have simply vanished into bigger ones. What follows are the largest US oil and gas companies measured by market capitalization, the total value of all their shares, as of mid-2025. One note before the list: market caps move every single day with the price of crude, so treat these figures as a recent snapshot rather than fixed numbers.

ExxonMobil

ExxonMobil is the largest oil and gas company in the United States by a wide margin, carrying a market value in the neighborhood of $450 billion, which also makes it one of the most valuable companies in the country across any industry. Headquartered in Spring, Texas, it is a fully integrated major, meaning it handles everything from exploration and drilling to refining and chemicals. The company traces back to John D. Rockefeller's Standard Oil and took its modern form in the 1999 merger of Exxon and Mobil. Its 2024 acquisition of Pioneer Natural Resources, a roughly $60 billion deal, dramatically expanded its footprint in the Permian Basin of West Texas and New Mexico, the most productive oil field in the country.

Chevron

Chevron is the second-largest US oil and gas company, with a market value generally in the $250 to $290 billion range. Like Exxon, it is a descendant of the broken-up Standard Oil empire and a fully integrated major, with operations spanning the Permian, the Gulf of Mexico, and projects across Africa, Asia, and Australia. Headquartered in San Ramon, California, Chevron spent much of 2023 through 2025 pursuing Hess Corporation in a roughly $53 billion deal that, after an arbitration fight with Exxon over a prized Guyana oil stake, finally closed and handed Chevron a share of one of the fastest-growing oil regions on earth.

ConocoPhillips

ConocoPhillips ranks third, with a market value in the area of $125 to $145 billion, and it is the largest US company focused purely on the upstream side of the business, exploration and production, without the refining and retail arms that Exxon and Chevron operate. Based in Houston, it was formed in 2002 from the merger of Conoco and Phillips Petroleum. Its biggest recent move was the 2024 purchase of Marathon Oil, which folded another major independent into its portfolio and deepened its position in US shale plays like the Eagle Ford, the Bakken, and the Permian.

EOG Resources

EOG Resources is one of the largest independent producers in the country, with a market value generally in the $70 to $80 billion range. Once a subsidiary of the failed energy-trading company Enron, EOG spun off and survived on its own to become a shale powerhouse, known across the industry for disciplined spending and an early, aggressive bet on horizontal drilling. Headquartered in Houston, it focuses on oil and gas production rather than refining, with core acreage in the Permian, the Eagle Ford, and other US basins.

Phillips 66

Phillips 66, the refining and midstream company spun out of ConocoPhillips in 2012, carries a market value in the rough vicinity of $50 to $60 billion. Rather than drilling for oil, it makes its money downstream, refining crude into gasoline, diesel, and jet fuel, moving natural gas liquids through pipelines, and running a chemicals joint venture. Based in Houston, it operates a network of refineries and thousands of branded fuel stations, which makes it one of the more visible names on this list to the average driver.

Williams Companies

The Williams Companies is a natural gas heavyweight, with a market value commonly in the $60 to $70 billion range. Williams is a midstream company, meaning it does not drill or refine so much as move product, and its crown jewel is the Transco pipeline, one of the largest natural gas transmission systems in the country, carrying gas from the Gulf Coast up the eastern seaboard. Headquartered in Tulsa, Oklahoma, Williams handles a sizable share of all the natural gas consumed in the United States.

Kinder Morgan

Kinder Morgan is one of the largest energy infrastructure companies in North America, with a market value often in the $55 to $65 billion range. Like Williams, it is a midstream operator, running an enormous network of pipelines and storage terminals for natural gas, crude oil, refined fuels, and carbon dioxide. Founded in 1997 by Richard Kinder, a former Enron executive, and based in Houston, the company controls tens of thousands of miles of pipeline that quietly keep fuel moving across the country.

Occidental Petroleum

Occidental Petroleum, widely known as Oxy, carries a market value generally in the $35 to $50 billion range and holds a special place in the industry as the company Warren Buffett's Berkshire Hathaway has been steadily buying into. Based in Houston, Oxy reshaped itself with the 2019 acquisition of Anadarko Petroleum, a deal that loaded it with debt but made it a Permian Basin powerhouse. Beyond drilling, the company has bet heavily on direct air capture technology, positioning itself as an unlikely player in carbon management.

Schlumberger

Schlumberger, which rebranded as SLB, is the largest oilfield services company in the world, with a market value generally in the $45 to $60 billion range. It does not own oil so much as the expertise and equipment to find and extract it, selling drilling technology, seismic imaging, and well services to producers around the globe. Though its operational roots are international and it maintains major hubs in Houston and Paris, it remains one of the most valuable energy companies tied to the US market.

Valero Energy

Valero Energy rounds out the group as one of the largest independent refiners in the world, with a market value commonly in the $40 to $50 billion range. Based in San Antonio, Texas, Valero turns crude into fuel rather than pulling it out of the ground, running more than a dozen refineries across the US, Canada, and the United Kingdom. It has also pushed into renewable diesel and ethanol, hedging the long-term decline that pure-play refiners eventually face.

The Leading US Oil And Gas Companies By Market Value

An Industry In Flux

The thread running through this list is consolidation. The biggest players have spent recent years buying their largest rivals, which is why familiar names like Anadarko, Pioneer, Marathon Oil, and Hess no longer appear on their own. What remains is a sector split between the integrated giants that do everything, the independents that only drill, the midstream companies that move the product through pipelines, and the service firms that supply the tools. Where any individual company sits from one quarter to the next depends heavily on the price of oil, so the rankings here are best read as a snapshot of a fast-moving business rather than a settled order.