The image that comes to mind is of the Pegasus, flying off into the sunset. But the reality isn't that stark. The Mobil brand with its bright red "o"s and its flying horse will still be around long after the company disappears from the corporate landscape.

The Federal Trade Commission yesterday cleared the last remaining hurdle to Exxon Corp.'s acquisition of the Fairfax-based oil company known not only for its gasoline but also for its "Masterpiece Theater" sponsorship and its advocacy advertising near the editorial pages of prestigious newspapers.

Mobil Corp. ends its corporate life a long way from where it was born, as a huge oil company that now becomes part of an ever greater behemoth, the world's biggest private energy company.

While Mobil, the company, is gone, its name may remain on some stations for five to 10 years after the merger, the FTC has decreed, in forcing Mobil to sell its interest in more than 1,500 service stations. The stations' new owners may need the clout of the Mobil name, the agency concluded.

The beginnings were humble. In 1866, a grocer named Hiram Bond Everest noticed a side-effect of an unsuccessful method of distilling kerosene in which he had invested $20. It produced an oily residue that became a major manufacturing lubricant marketed by a company Everest named Vacuum Oil Co.

In 1879, John D. Rockefeller's Standard Oil Co. bought a three-quarter interest in Vacuum for $200,000. But in 1911, federal regulators broke up Rockefeller's massive Standard Oil Trust, spinning off 33 companies, including not only the company that would become Exxon, but also Vacuum and Standard Oil of New York (Socony), which would merge in 1931. Not long after, a trademark was issued for the use of Mobil, a word that was coined, according to Mobil's corporate history, by knocking the suffixes off "Mobiloil" (marketed as early as 1899) and "Mobilgas."

In 1955 the company became Socony Mobil Oil Co. Inc., and then in 1966, when the company was 100 years old, its name was changed to Mobil Oil Corp.

The Mobil of today is largely a creature of an expansionary surge following the oil shocks of the 1970s, when companies concluded it was cheaper to buy rivals' oil and gas supplies than to search for new reserves.

Mobil also began two of its most successful public relations initiatives in the 1970s, launching its high-profile ads commenting on issues ranging from U.S. sanctions against Iran to support for the arts to the use of seat belts in 1972. Over the years, it has run more than 1,400 of the ads. It also began its sponsorship of "Masterpiece Theater" on PBS in 1970.

The 1970s also witnessed the beginning of a long-running legal dispute between Mobil and The Washington Post over a newspaper article about the business activities of the son of Mobil's then-president, William P. Tavoulareas. A jury found in July 1982 that the paper had libeled Tavoulareas, but the verdict was overturned on appeal.

As Mobil grew, it found that New York City was becoming a hard sell for new employees, and in 1977 it moved a major division to Fairfax County, followed by its corporate headquarters 10 years later.

Mobil's arrival as the Washington area's largest corporation coincided with the beginning of an economic growth surge in Northern Virginia that continues today.

The 1990s are ending with another wave of consolidation in the oil industry led by giants the size of Mobil and Exxon, which have determined that they must be bigger to save money, to compete more aggressively for oil and gas reserves and to be a contender in a world oil market that includes huge state-owned oil companies such as Saudi Aramco.

Yesterday, with the vote of the FTC and the filing of documents in New Jersey and Delaware, Mobil became a wholly owned subsidiary of Exxon, now named Exxon Mobil Corp.

CAPTION: Mobil's corporate insignia, Pegasus, has been a familiar sight on Gallows Road.