The headlines have been piling up: More and more passenger airlines have introduced new fees and charges for checked baggage, as a way to help offset the rising cost of aviation fuel.

Check: Delays | On-Time Performance | Baggage Fees

But who charges what? Here are the current checked-bag fees for the 10 busiest U.S. carriers for 2007, as ranked by the Department of Transportation.

1 Southwest

The first and second checked bags on Southwest are free. The third checked bag costs $25. The fourth bag costs $50 and every bag after that costs $110 each. The overweight limit begins at 51 pounds. Bags weighing 51 to 70 pounds cost $25. Bags weighing 71 to 100 pounds cost $50. The Southwest oversize limit starts at 63 inches. Each bag measuring 63 to 80 inches on the longest side costs $50. The carry-on limit is 50 inches; there's no weight specification. (More details at Southwest.)

2 American

The first checked bag on American Airlines is $15. The second is $25. Three to five checked bags will cost you $100 each. A sixth bag will cost $200. There is no weight charge for bags 50 pounds or less. Bags weiging 51 to 70 pounds will cost $50. Bags weighing 71 to 100 pounds will cost $100. American's oversize limit begins at 63 inches. Bags measuring 63 to 115 inches on the longest side cost $150. The carry-on size limit is 45 inches and 40 pounds. (More details at American.)

3 Delta

The first checked bag on Delta domestic flights is free. The second domestic bag costs $50 and the third is $125. On international flights the first and second checked bags are free. The third to the 10th bag costs from $150 up $600 each. There is no weight charge for bags weighing up to 51 pounds. Bags weighing 51 to 70 pounds cost $90 each. Bags weighing 71 to 100 pounds cost $150 each. Delta's oversize limit begins at 62 inches. Bags measuring 62 to 80 inches on the longest side cost $175 each. The carry-on limit is 45 inches and 40 pounds. (More details at Delta.)

4 United

On its domestic flights, United charges $15 for the first checked bag, $25 for the second and $125 for the third; anything more than that costs $250 each. Its international rate vary. The overweight limit on checked bags starts at 51 pounds. Bags weighing 51 to 100 pounds cost $125 each. The oversize bag limit begins at 63 inches. Bags measuring 63 to 115 inches on the longest side cost $125 each. The carry-on size limit is 45 inches; there's no weight specification. (More details at United.)

5 Northwest

The first checked bag on Northwest costs $15. The second costs $25. The third costs $100. The overweight limit starts at 51 pounds. Bags weighing between 51 to 70 pounds cost $50. The size limit on checked bags starts at 63 inches. Bags measuring 63 to 80 inches on the longest side cost $100; the rate varies on international flights. The carry-on limit for Northwest is 45 inches; there's no weight specification. (More details at Northwest.)

6 Continental

The first checked bag on Continental is free. The second costs $25. The third costs $100. There is no weight charge for bags 50 pounds or less. Bags weighing 51 to 70 pounds cost $50. American's oversize limit begins at 63 inches. Bags measuring 63 to 115 inches on the longest side cost $100. American's carry-on limit is 51 inches and 40 pounds. (More details at Continental.)

7 US Airways

The first checked bag on US Airways costs $15, the second costs $25. The third bag and any more after that cost $100 each. The overweight limit starts at 51 pounds. Bags weighing 51 to 70 pounds cost $50 to $150. Bags weighing 71 to 100 pounds cost $100 to $200 (based on number of bags). The oversize limit starts at 62 inches. Bags measuring 62 to 80 inches on the longest side cost $100. The carry-on limit is 51 inches, with no weight specified. (More details at US Airways.)

8 AirTran

The first checked bag on AirTran is free. The second is $10 if checked online, or $20 at airport. A third is $50. There is no weight charge for bags 50 pounds or less. Bags weighing 51 to 70 pounds cost $29. If they weigh 71-100 pounds, they cost $69 extra each. AirTran's oversize-bag limit starts at 62 inches. For bags measuring 62 to 70 inches on the longest side there's a $29 charge. For bags 71 to 80 inches the charge goes up to $69. The airline's carry-on limit size is 55 inches, with no weight specified. (More details at AirTran.)

9 SkyWest

SkyWest serves as a feeder airline. It flies as United Express on behalf of United Airlines, as Delta Connection on behalf of Delta Air Lines, and as Midwest Connect on behalf of Midwest Airlines. Baggage fees for individual feeder airlines apply. Follow these links for details: United, Delta, Midwest.

10 JetBlue

On JetBlue, the first chacked bag is free. The second costs $10 and the third costs $75. First: free. Second: $10. Third: $75. The overweight bag limit starts at 51 pounds, with bags weighing 51 to 70 pounds costing $50 and bags weighing 71 to 99 pounds costing $100. The oversize bag limit starts at 63 inches, with bags measuring 63 to 80 inches costing $75 each. The carry-on limit is 50 inches for smaller Embraer 190 planes, and 56 inches for larger Airbus A320s, with no weight specified. (More details at JetBlue.)