Chevron, based in San Ramon, runs California's two largest oil refineries, in El Segundo and Richmond. It's the state's top oil producer and one of the largest producers of natural gas.
Here's a look at some of its key moments in its history:
Chevron traces its history to 1879 when Pacific Coast Oil Co. was founded.
In 1906, a consolidation between Pacific Coast Oil and Iowa Standard created a new entity, Standard Oil Co.
Then in 1911, Standard Oil was broken into several pieces under the Sherman Antitrust Act. One of those pieces, Standard Oil Co. of California, or SoCal, went on to become Chevron.
Today, Chevron is the owner of the Standard Oil trademark in 16 states in the western and southeastern U.S.
In 2001, the company merged with Texaco, changing its name to Chevron Texaco Corp., but by the time it acquired Unocal Corp. in 2005, it had dropped the Texaco name.
Chevron could be forced to up its offer to billions more should it decide to sweeten the deal.
Chevron is the world's third-largest publicly traded energy company in market capitalization.