Oil refiners Valero Energy Corp. and Marathon Petroleum Corp. are the biggest beneficiaries of the U.S. government's oil reserve releases, taking nearly half the crude offered, a Reuters analysis of Department of Energy data showed on Sept. 21.

The Biden administration has opened spigots at the nation's Strategic Petroleum Reserve (SPR) to lower fuel prices and ease a supply crunch from Russia's invasion of Ukraine. Awards of about 218 MMbbl for the 12 months ended Sept. 30 have tamed market worries and cut energy prices.

But they have slashed the reserve to 427.2 MMbbl - or about four weeks of demand - the lowest level in about 38 years. This has sparked criticism because some oil was resold to buyers overseas. A few distributions came under congressional mandates while others are pending.

The two biggest receivers acquired nearly 98 MMbbl so far. Valero, the second largest U.S. refiner by capacity, secured 52.7 MMbbl, while top oil processor Marathon Petroleum snapped up 45.2 MMbbl.

Other big buyers included Exxon Mobil, with 24.7 MMbbl, Motiva Enterprises at 22.1 MMbbl, Shell at 15.2 MMbbl and Phillips 66 at 16 MMbbl.

Marathon Petroleum declined to comment on crude sourcing. Other companies did not immediately respond to requests for comments.

Some of the barrels were exported by Exxon Mobil, Phillips 66, TotalEnergies' trading unit Atlantic Trading and Marketing as well as Unipec, an arm of Asia's largest refiner Sinopec, according to U.S. Customs data.

Most of the oil was sold via auctions at prices determined by a five-day average around the date of delivery. A smaller quantity was exchanged and typically requires receivers to replace the oil with a slightly larger volume.

About 24.42 MMbbl were released by exchange, with the largest amounts taken by Exxon and Shell.

The SPR will be replenished via contracts to purchase oil in the future at fixed, preset prices. The plan would help boost oil production, the administration said.