Shell Oil Company is a wholly owned subsidiary of Royal Dutch Shell.
Prior to 1984, Shell Oil was traded on the NYSE and was mostly independent from Royal Dutch Shell. However, in 1984, Royal Dutch Shell bought all outstanding shares it did not own, at a value of $5.7 billion.
Shell Oil has remained somewhat independent from Royal Dutch Shell. Prior to 1998, the logo used in the US was different from the worldwide logo.
In 2008, the company was sued for being in violation of the Clean Air Act.
Today, Shell Oil is one of the largest oil companies in the world. There are over 25,000 Shell gas stations in the US.