CHICAGO —  United Airlines has doubled its fee for a second checked bag to $50, citing volatile fuel prices.

United says the $50 one-way fee will apply for tickets bought beginning Tuesday for travel beginning November 10 within the U.S. or to or from Canada, Puerto Rico and the U.S. Virgin Islands.

Travelers in first or business classes, "Premier" frequent fliers and active-duty military personnel traveling on orders will be exempt. United estimated the $50 fee would apply to about one out of every seven customers.

Fuel prices have declined in recent weeks as oil prices have fallen, from a high of $147 a barrel to below $96 a barrel on Monday. But United says fuel prices remain more than 50 percent higher than last year.