United Airlines said on Friday it raised round-trip fares by USD$6 and one-way tickets by USD$3 on some routes where it faces low-cost competition.
A spokeswoman for United said the carrier increased the prices on Thursday night to offset the higher cost of fuel.
US carriers have implemented several fare increases this year to combat high fuel prices. United spokeswoman Robin Urbanski said that despite a recent decline in fuel prices, fares in some markets are still too low.
The price of crude oil -- directly linked to the price of jet fuel -- has fallen more than 20 percent since August, but the price remains historically high and a burden for airlines. On Friday, crude was trading at USD$60.78 a barrel.
American Airlines matched United's increase on Friday morning, an AMR spokesman said. Bankrupt Delta Air Lines said it also has matched the increase. Continental Airlines said it has not matched.
It remains to be seen whether the fare increases will last. Earlier this month, several airlines rescinded increases that went unmatched by a broad base of competitors, according to industry sources.