What are the four major American automobile companies?

I've only heard of the Big Three. Where did you get the four big companies?

They are General Motors, Ford and Chrysler.

GM's brands are:

Chevrolet, Buick Buick, Pontiac Pontiac, GMC, Saturn, Hummer, Saab Saab, Cadillac.

Ford's brands are:

Ford Ford, Lincoln, Mercury, Mazda, Volvo, Jaguar, Land Rover and Aston, Martin Aston Martin.

Chrysler has:

Chrysler Chrysler, Dodge Dodge and Jeep Jeep.

If we can find other American cars, by the way, it may be the fourth largest factory!