The Federal Trade Commission on Friday cleared the way for Chevron Corp. (CVX) to acquire Unocal Corp. (UCL) for $18 billion, voting 4-0 to settle a two-year-old complaint against Unocal alleging anticompetitive practices.

The settlement ends a legal fight between Unocal and the FTC (search) over the energy company's rights to a patent for reformulated gasoline.

The regulatory agency said the key element of the settlement is Chevron's agreement not to enforce patents of a Unocal subsidiary that could have increased gasoline prices in California by over half a billion dollars a year, or almost six cents a gallon.

The FTC's long-standing complaint alleged that Unocal subsidiary Union Oil illegally acquired monopoly power in the technology market for producing low-emission gasoline mandated by the state of California.

The complaint said Union Oil misrepresented to the California Air Resources Board (search) that certain gasoline research was non-proprietary and in the public domain, while simultaneously pursuing a patent that would enable it to charge substantial royalties if CARB used the research results in developing regulations.

Chevron announced in April the agreement to acquire Unocal.

Chevron explores for, refines and transports crude oil and gas. Unocal's operations are in exploration and production of crude oil and natural gas, with no refineries or gasoline stations. Together the two companies have over 11 percent of U.S. crude oil production.

FTC Chairman Deborah Platt Majoras recused herself from voting on the matter.