Phillips Petroleum Company was an American oil company incorporated in 1917, that expanded into petroleum refining, marketing and transportation, natural gas gathering and the chemicals sectors. It was Phillips Petroleum that first found oil in the North Sea on December 23, 1969, at a position that was later named Ekofisk.

On August 30, 2002, Conoco Inc. merged with Phillips Petroleum to form ConocoPhillips, becoming the third largest integrated energy company and second-largest refining company in the United States. The company moved its headquarters to Houston.

In 2012, ConocoPhillips split into two separate companies. The legacy company kept its name, and spun off the midstream and downstream portions of its business. The new company, which owns the refinery, chemical and pipeline assets formerly held in ConocoPhillips, is named Phillips 66, the brand name and trademark used by the original Phillips Petroleum from 1930 until the 2002 ConocoPhillips merger.

The Phillips Petroleum Company was incorporated on June 13, 1917, by brothers Lee Eldas ("L.E.") Phillips and Frank Phillips, of Bartlesville, Oklahoma, United States. Their younger brother, Waite Phillips, was the benefactor of Philmont Scout Ranch. The company was headquartered in Bartlesville, Oklahoma.

Phillips Petroleum rapidly became a fully integrated oil company that included oil and gas production, crude oil pipelines and refineries, and marketing of petroleum products.

Phillips Petroleum became heavily involved in the natural gas industry immediately after the discovery of the Panhandle gas field of Texas and the Hugoton field in Kansas. By 1925, it was the largest producer of natural gas liquids (NGL) in the United States.

In 1927, Phillips started up its first petroleum refinery in Borger, Texas, designed to produce gasoline as an automotive fuel. The refinery also produced other petroleum fractions (e.g., kerosene, fuel oils). It opened its first service station, to sell gasoline, in Wichita, Kansas on 19 November 1927. In 1930, the company developed its "Phillips 66" trademark: according to company lore, a Phillips official was road-testing the company's newest gasoline, commented that the car was going "like 60" when his driver replied "Sixty nothing ... we're doing 66!", all while driving on U.S. Highway 66 in Oklahoma near Tulsa, resulting in the number 66 superimposed on the U.S. Highway symbol for Route 66.

Frank Phillips served as president of the company until 1938. He then turned over the presidency to Kenneth S. "Boots" Adams, but continued as chairman of the board until 1949, when he was 76 years old.^{[citation needed]}