Rising fuel costs aren?t just affecting travelers at the pump anymore ? people who travel by air are now paying the price as well.

Many airlines are adding additional fees for customers who have extra baggage or want to choose where they sit. Three weeks ago, American Airlines began charging $15 for a passenger?s first checked bag, and beginning Friday, United Airlines will add a $15 fee to tickets for passengers flying domestically on or after Aug. 18.

U.S. Airways is also adding a baggage fee, which kicks in for tickets booked on or after July 9. The airline also cut costs by cutting out free snacks, such as pretzels and peanuts, from its coach section. Non-alcoholic drinks, which used to be complimentary, will soon be offered for a fee.

Additional fees for seat reservations may be next. Spirit Airlines is already charging $5 for middle seats, $10 for window seats and $15 for exit-row seats.

Southwest Airlines allows passengers to check two bags for free, and as of July 1, it will be the only U.S. carrier permitting passengers to do so. Many airlines already have a $25 fee for a second checked bag.