It's a frustrating hurdle on the way to a long-planned vacation: You wedge your family of five's clothes and gear into coffin-sized roller bags to minimize hassles at the airport and shuffle through the cattle lines to the check-in counter only to discover at the last minute that one of your stuffed-to-the-gills bags is one pound -- and almost $100 -- overweight.

What do you do? In our case, stymied at the Minneapolis-St. Paul airport on our way to a week of Colorado skiing and snowboarding, and holding up a line of passengers with grim faces and set jaws, we made some quick calculations. Do we just pay the overweight charge? We do not (sorry mister airline accountant). Do we run and buy another bag to distribute the weight better? That's a time suck that isn't practical because the shops are all on the other side of the massive security screening funnel. Do we haul out a pair of ski boots and carry them as hand luggage? Nix that: We're already at our carry-on limit. Our best option was to get the (very nice and helpful) ticketing agent to weigh both bags. We found that the extra weight in one could be offloaded into the other, which was 5 pounds under the limit.

Mission accomplished. But we could have avoided the hassle if we had simply paid attention to our carrier's weight restrictions on checked bags.

Who charges what? Here are the current fees for the 10 busiest U.S. carriers as of January 2009, ranked by the Department of Transportation. The fees quoted below generally apply to a single passenger traveling coach class one way in the 50 U.S. states, and in some cases Puerto Rico, Canada and the U.S. Virgin Islands. Also, some airlines offer frequent flyers and award program members a break on baggage fees. Be sure to follow the links to find more details.

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.)

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 weighing 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.)

Delta

The first checked bag on Delta domestic flights costs $15. The second domestic bag costs $50. The third costs $150. On international flights the first and second checked bags are free. The third to the 10th bag costs from $200 up $600 each. There is no weight charge for bags weighing up to 50 pounds. Bags weighing 51 to 70 pounds cost $90 each ($150 outside the U.S.). Bags weighing 71 to 100 pounds cost $175 each ($300 outside the U.S.). Delta's oversize limit begins at 63 inches. Bags measuring 63 to 80 inches on the longest side cost $150 each. Larger sizes are not permitted. The carry-on limit is 45 inches and 40 pounds. (More details at Delta.)

United

On its domestic flights, and flights to Canada and the U.S. Virgin Islands, United charges $15 for the first checked bag, $25 for the second check bag each way. Its international rates vary, and there are price breaks for some frequent-flyer program members. 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 on carry-ons. (More details at United.)

US Airways

The first checked bag on US Airways costs $15, the second costs $65. A bag weighing 51 to 70 pounds costs $65; a second overweight bag costs $75. A first bag weighing 71 to 100 pounds costs $115; a second bag in that range costs $125. The oversize limit starts at 62 inches. Bags measuring 62 to 80 inches on the longest side cost $100. The carry-on size limit is 14 x 9 x 22 inches, and 40 pounds. (More details at US Airways.)

Northwest

The first checked bag on Northwest costs $15. The second costs $25. The third costs $125. The overweight limit starts at 51 pounds. Bags weighing 51 to 70 pounds cost $90. Bags weighing 71 to 100 punds cost $175. 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, and bags measuring in excess of 80 inches on the longest are not accepted. The carry-on limit for Northwest is 9 x 14 x 22 inches; there's no weight specification. (More details at Northwest.)

Continental

The first checked bag on Continental costs $15. 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. Continental's oversize limit begins at 63 inches. Bags measuring 63 to 115 inches on the longest side cost $100. Continental's carry-on limit is 41 linear inches (length by width by height) and 40 pounds. (More details at Continental.)

AirTran

The first checked bag on AirTran is $15. 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 $39. If they weigh 71-100 pounds, they cost $79 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 $39 charge. For bags 71 to 80 inches the charge goes up to $79. The airline's carry-on limit size is 55 inches, with no weight specified. (More details at AirTran.)

JetBlue

On JetBlue, the first checked bag is free. The second costs $20 and a third or more costs $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. Anything longer won't be accepted. The carry-on limit is 24 inches for smaller Embraer 190 planes, and 26 inches for larger Airbus A320s, with no weight specified. (More details at JetBlue.)

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.