Between 1921 and 1922, Sinclair leased oil production rights to Teapot Dome in Wyoming without competitive bidding.

[9] As the Teapot Dome scandal unfolded in the United States and reached the international press, Mussolini accelerated the negotiations, with a deal signed on May 4, 1924 (although without an official meeting, to avoid public outcry).

[10] The deal was reported in a press release by the Head of Government (Mussolini) issued on the night of May 15, 1924, and published by most newspapers on the following day.

[11] This case of corruption was reported by the anti-fascist politician Giacomo Matteotti - who was later kidnapped and killed by Mussolini's newborn secret police, just before he could report his discoveries to the Parliament — in his posthumous article, published in the July issue of English Life (a magazine founded by Brendan Bracken): Matteotti accused Sinclair Oil of being a pawn of Standard Oil, as well as revealing "grave irregularities concerning the concession.

[14] During the Great Depression, Sinclair saved many other petroleum companies from receivership or bankruptcy and acquired others to expand its operations.

Lastly, in 1936, Sinclair purchased the East Coast marketing subsidiary of Richfield Oil Company, which had operated in receivership for several years.

[19][21][22] Two of the replicas (Tyrannosaurus and Brontosaurus) are still on display at Dinosaur Valley State Park near Glen Rose, Texas.

A copy of the Triceratops is also owned by the Smithsonian Institution and is on display as "Uncle Beazley" in the National Zoological Park in Washington, D.C.[26] In 1955, Sinclair ranked 21st on the Fortune 500; by 1969, it had fallen to 58th.

[27] In 1969, Sinclair merged with the Atlantic Richfield Company (ARCO) after an attempted acquisition by the Gulf+Western Industries Corporation.

In the mid-2010s, Sinclair fuel stations began actively spreading across southern California, including Los Angeles, San Diego, and Fresno, with holders offering attractive deals for potential clients to make the switch from a private brand to the Sinclair name brand.

[29] By 2018, Sinclair gas stations were widely distributed across the United States, with dozens of gas stations in California, Colorado, Iowa, Idaho, Minnesota, Missouri, Montana, Nebraska, Nevada, Oklahoma, Oregon, South Dakota, Utah, and Wyoming; smaller numbers in Arizona, Connecticut, Kansas, Kentucky, North Dakota, New Mexico, New York, Texas, and Washington; and a single station in Arkansas and Wisconsin.

It was expected that the vast majority of Sinclair Oil employees would be invited to continue in their positions following the combination.

Terminals were located in: Sinclair also owned and operated Grand America Hotels & Resorts, which has hotel properties in Salt Lake City, Utah; Flagstaff, Arizona; Cheyenne, Wyoming; Little America, Wyoming; and San Diego, California, in addition to the Sun Valley and Snowbasin ski resorts.

In March 2022, the sale to HollyFrontier was completed, and HF Sinclair Corporation traded on the NYSE under the ticker symbol DINO.

[34] The Brontosaurus logo is parodied in the Toy Story and Cars franchise films as being the "Dinoco" gas station chain, perhaps an allusion to gasoline and its origin as a fossil fuel, as well as a portmanteau between the "dinosaur" in Sinclair's logo and the suffixes of the "Amoco", "Conoco", and "Sunoco" franchises.

[citation needed] The TV series Dinosaurs featured several characters with names derived from fossil fuel companies.

Joey Jordison, founding drummer of Slipknot, worked at a Sinclair's garage in Urbandale, Iowa, where late at night the band would discuss their plans.