Gasoline Free Market Competition Act of 2003 - Amends the Clayton Act to prohibit any person engaging in commerce from: (1) imposing any condition, agreement, or understanding between a crude oil refiner and a motor fuel distributor that limits or prevents the distributor from supplying branded gasoline to independent motor fuel retailers in a highly concentrated market, unless the limitation can be proven not to injure, destroy, or limit competition; (2) selling the same brand of gasoline (if that person is a refiner) to retailers owned or controlled by that refiner in a highly concentrated market at different prices than the refiner charges to its independent dealers, or selling to independent dealers in the same relevant geographic market at different prices if those dealers are located in a highly concentrated market; or (3) engaging in any other practice that the Federal Trade Commission (FTC) determines would be likely to reduce supply or increase the price of gasoline in a highly concentrated market.

Directs the FTC or the Attorney General to provide notice to each refiner, distributor, and retailer doing business in a highly concentrated market that such market is a "consumer watch zone" subject to specified conditions.

Prohibits the FTC or the Attorney General from approving any combination that would create a highly concentrated market that would injure, destroy, or limit competition.

Authorizes State attorneys general to bring civil actions in U.S. district court.