why is ford considered an oligopoly?

Answer 1

It actually is NOT considered an oligopoly anymore.

Back when the US auto industry was dominated by the "Big Three" (GM, Ford, Chrysler), it was considered an oligopoly because the entire industry was controlled by three companies that often based prices on each others' prices.

Since the 1980s, the explosion of "foreign" car makers has destroyed the Big Three's hegemony. In fact, Chrysler almost went under in the late 80s, Ford is collapsing now, and GM is bleeding cash so fast they might be bankrupt within a decade.

Answer 2

Yeah, it ain't. These days in the US, Ford is just one of about 15 mainstream competitors in a competitive market, it's status falling fast.