Airlines are imposing hefty penalties for heavy baggage. Some charge simply for the privilege of checking luggage.

Here are brief policy summaries for 10 leading low-cost carriers.

If your airline is not listed here, go to the home page of its Web site, click on a link (usually in small print) for "Site Map" and then find baggage fees. Every attempt is made to update the summaries, but these policies change quickly. Read them carefully on the linked Web sites.

1.Southwest Airlines

Southwest allows two free checked bags per customer. The maximum weight for baggage is 50 lbs. Overweight items from 51-100 lbs. and oversized items (62-80 in.) incur a charge of $50/item. Any item weighing more than 100 pounds must be shipped as Air Cargo, and that availability is limited. Your 3rd through 9th bags will incur a charge of $50 per piece, and any bag or item thereafter will be $110 per piece.

2. Ryanair

Ryanair allows you one carry-on bag (weighing up to 10 kg or 22 lbs.) on each flight. Checked baggage charges vary depending upon when passengers choose to pay the fees. For example, the baggage fee per passenger, per one-way flight for the first bag is a flat £10 or €10 when booked on ryanair.com, but £20 or €20 per item when arranged through a call center or at the airport. Second and third bags are £20 or €20.

3. Gol

This link takes you to a page written in Portuguese. Each adult passenger is entitled to check as many as two pieces of luggage weighing a total of 23 kg. (51 lbs.) For each kilogram above the limit, a fee is of 0.5% of the normal economy class fare is charged. Baggage with excess weight is treated as cargo and might be shipped on a separate flight.

4. easyjet

Each passenger is allowed one piece of carry-on baggage not to exceed 55x40x20cm. Any checked baggage will incur a fee. Paying the fee at time of booking can result in a discount. Charges are made up to a maximum of 50 kg. (110 lbs.), with no single bag heavier than 32 kg. (71 lbs.) Where checked-in hold baggage exceeds 20 kg., each passenger pays an excess baggage charge per kg. of £9 or €12. There is also a fee structure for larger sporting equipment such as skis or golf clubs.

5. jetBlue

Passengers are allowed one carry-on bag that must be stored in an overhead compartment. One checked bag and one stroller are permitted without charge so long as size requirements are met. A second checked bag requires a $30 fee. The third bag incurs a $75 fee. Starting at 100 lbs., bags are ineligible for acceptance on the flight. Charges are also made for large items, regardless of weight.

6. Virgin Blue

Each Guest traveling on Blue Saver or GO! fares will have the option of purchasing a checked baggage allowance of up to 23 kg. (50 lbs.) for $8 AUD per flight at time of booking. If you must check a bag of up to 23 kg. at the airport, a fee of $20 will apply. Each piece of baggage must not weigh more than 32 kg. (70 lbs.) and must not exceed a total linear dimension of 140 cm. (55 in.) when adding together depth, width and length. There is a $10 charge for each kilogram in excess of the limit.

7. AirTran

AirTran passengers are permitted one carry-on one bag (under 55 in.) and one personal item. The first checked bag costs $15 USD; a second is $25, a third $50. Overweight baggage rates: $39 for each bag weighing 51-70 lbs., and $79 for each bag weighing 71-100 lbs. Baggage weighing over 100 lbs. will not be accepted. Active military personnel traveling with ID and official orders will have fees waived for up to three bags, and the oversize and overweight fees for those three bags.

8. Westjet

Two carry-on bags (weighing up to 10 kg. or 22 lbs.) are permitted free of charge. In addition, two checked bags (weighing up to 27 kg. or 60 lbs.) are allowed without charge. Extra pieces beyond these amounts incur a fee of $75 USD/item. A maximum of two excess pieces will be accepted on a space-available basis only per fare-paying guest. Overweight and oversize pieces are carried for a fee of $50/item. Excess baggage must be processed no later than one hour prior to departure.

9. Air Berlin

Air Berlin allows only one carry-on item, and unless it's a laptop, it must not weigh more than 6 kg. (13 lbs.) Economy class passengers may check in two items of baggage weighing up to 23 kg. (51 lbs.) each, and business class passengers to check in two items of baggage weighing up to 32 kg. (70 lbs.) each. The sum of the height, length and width must not exceed 158 cm. (62 in.) Exceed the limit and you'll pay fees ranging from $25 USD (25 EUR) to $450 (450 EUR).

10. Spirit Airlines

Spirit allows one carry-on and one personal item in the cabin. Spirit does not provide free checked baggage, and charges an online fee of $19 USD for the first piece ($6 more at the airport). Spirit does not guarantee it will sell passengers space for additional checked bags, so plan to bring those at your own risk. When available, the fees: a second item is $25; Items three, four and five will each cost $100. Overweight bags between 50-71 lbs. cost $50; 71-99 lbs. cost $100. Oversize fees regardless of weight: over 62 in. is $100 and over 80 in. is $150.