American Airlines (AMR) will soon charge us an additional $30 for checking a bag on a round-trip flight. Why not just raise its fares as fuel prices rise and spare us a more cramped cabin?

Because--let's face it--a good chunk of us go online, find the lowest fare on a flight aggregator like Orbitz ( OWW) or Expedia ( EXPE), and buy our ticket. Forget the airline's record with most on-time flights. Who cares if there's in-flight entertainment? We see a flight from Milwaukee to New York for $69, we're buying it.

For airlines, fees are a way to game the system. Sure, one airline may charge $69 for its base fare, but tack on baggage fees, reservation fees and the cost of peanuts. Soon, you may be paying more than you would for a flight that, at first glance, looks more expensive.

So how do you avoid being taken? Here's a rundown of questions to answer before you assume the ticket with the lowest fare is going to end up costing you the least. Fees apply to domestic flights, and many can be avoided if you belong to an elite travel club, pay full fare or buy unrestricted tickets.

But for those of us looking for a deal, here's a rundown of how to get the best deal.

How much is the first bag going to cost me?

Alright, so only American Airlines has announced plans to charge for the first bag of stowed luggage. But after June 15, it'll cost most of us an additional $30 if the bag's traveling round-trip. If you're thinking, "I'll just pack my one carry-on bag extra tight," remember, everyone else is thinking the same thing. Even if you can cram all your stuff into the one bag, you might want to consider shelling out a few extra bucks for a flight where each passenger isn't desperately trying to carry as much on board as possible.

What will additional bags run me?

Even if you head out with only one bag, many of us have a way of accumulating knick-knacks along the way. So if you're likely to go crazy buying Kachina dolls on your trip to Santa Fe, you might want to know ahead of time what bringing back an extra sack full of crafts is going to cost you.

Virtually everyone is charging $25 each way for a second piece of checked baggage. Notable exceptions: A second bag is free on Southwest Airlines ( LUV), and JetBlue ( JBLU) will charge only $20 starting June 1 (currently it's free). And AirTran ( AAI) charges $20 for your second checked bag unless you pay using Online Check-In, where the fee is cut in half.

Are my bags overweight?

Anyone thinking they can game the system with that huge piece of luggage in their closet, think again. Checked luggage has both size and weight limitations.

Typically, you're limited to 50 pounds per piece of checked luggage and the length, width and height can't exceed 62 inches.

If your luggage weighs more than 50 pounds but no more than 70 pounds, fees are generally in the $50 range. But Southwest and AirTran charge significantly less: $25 and $29 respectively. And Delta at $80 and United at $100, charge more.

Luggage weighing more than 70 pounds may not be accepted by all airlines. Those that do generally charge $100 for bags up to 100 pounds. The outliers are Southwestern (which charges $50) Airtran ($69) and (on the high side) Delta ( DAL) ($150).

Oversized luggage is going to cost you, too: anywhere from $29 (Airtran up to 80 inches) to $150 (Delta up to 80 inches).

Just as a super-big bag's going to cost you, so is bringing a bunch of smaller ones. An extra bag on a typical airline will run you $100. But at $25 for the third bag and $50 for the fourth through ninth bag, Southwest has the lowest fees; Airtran, JetBlue ( JBLU) and Delta also have below-average fees.

What does it cost to make/change a reservation?

If you're booking through a service that aggregates fares from various airlines, the service charge (if any) will be the same, no matter the airlines, so ticket prices are apples-to-apples comparisons.

If you find a fare you like and try to pick up the phone to book it directly through the airline, your fees will vary, although booking a ticket through an airline's Web site is typically still free. If you call, fees will run you from $10 (AirTran) to $25 (Delta). Southwest doesn't have a fee at all, but it warns you: cheaper fares may be available online.

After you have a reservation, if you buy a cheap ticket, changing it is likely to cost you. Continental ( CAL), United ( UAUA), US Airways ( LCC) and American Airlines all charge -- or will soon charge -- a whopping $150 fee in addition to any fare increase.

On the low end, AirTran charges only $75. Southwest charges only the fare increase -- which may be significant if you reserved your ticket well in advance of flying.

Am I likely to get the munchies?

If it's a long flight and you're like most of us, the answer is "Yes." And increasingly, salt cravings are going to cost you -- a 4 oz. bag of nut blend on American Airlines costs $3.

And even when your bag of peanuts -- or, in JetBlue's case, Terra Blues potato chips -- come free, chances are you won't get a full free meal on a domestic flight. Those airlines that serve meals typically charge between $6 and $8 (though Continental gives you a complimentary meal on flights over three hours).

Buying food is cheaper than bringing extra baggage, but it's still a hefty price for airline food.

The good news: a can of Coke brought from home may be deemed a security hazard, but you'll probably be able to bring a home-cooked (or restaurant-bought) meal onto the plane.

Will I shell out for entertainment?

If there's a movie and you've forgotten your headphones, a disposable set from the airline is likely to set you back a buck or two. Some airlines -- like Southwest -- don't offer in-flight movies. Some movies will cost you too: if you've got your own TV screen, you can bet the airline's found a way to get you to pay a few more bucks.

But escaping these added fees is easy--bring your own headphones and mp3 player or (gasp) a book.

How much do I want to sit next to other people's kids/pets/bags?

We may hate fees when they're applied to us, but sometimes, when applied to others, fees are entirely welcome. Who wants to sit next to someone else's unaccompanied five-year-old or a yipping dog?

Most airlines charge $100 for flyers to bring Spot onboard. Continental ($95), Northwest ( NWA)($80) and AirTran ($69) are the exceptions. But if you want to be sure you're not sitting next to Fluffykins when it starts mewling two hours into a five-hour flight, fly Southwest, which doesn't allow pets onboard at all.

Children, however, are another story. Southwest doesn't charge additional fees for unaccompanied minors (most charge $75 to $100), while AirTran costs only $39 to $69.

Of course, our list of fee-uncovering questions isn't comprehensive. If your airline's nickel and diming you on headphones, don't be surprised if they try and charge you for a blanket -- or force you into the bathroom if you're riding free on a buddy pass. But if the fees on your flight start piling up, consider another carrier: better the base fare you know than the fees you don't.

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