(CNN) -- It may seem like airlines have thought of every possible way to squeeze more money out of air travelers, charging extra for everything from early boarding to checking bags.
But hold on to your wallet: There's probably room for more fees. Might you eventually pay for holding your baby on your lap during a flight? Or talking to an airline employee during check in?
The trend of a la carte pricing -- charging rock bottom prices for base fares, then adding fees for anything extra -- helped domestic airlines deliver the biggest profits in a decade last year.
The industry collected $2.1 billion in fees during the third quarter of 2010 alone, according to the Bureau of Transportation Statistics. That includes more than $900 million in baggage fees and almost $600 million in reservation change fees.
"I think (airlines) are addicted to the fees," said George Hobica, the founder of Airfarewatchdog.com. "They're always thinking about new fees because that's how they make money."
No wonder carriers may be tempted to come up with even more extra charges for fliers.
What exactly might they be? Hobica recently put together a list of possibilities for 2011 and it's not pretty.
But be aware that he based some of his guesses on fees already being charged in Europe, especially by low fare champ Ryanair, which may not materialize any time soon in the United States.
"Ryanair wants to charge to use the restroom," said Tom Parsons, CEO of BestFares.com, referring to the infamous idea floated by the carrier in recent years. "I don't think that's going to happen either."
With that in mind, here are some of Hobica's predictions:
Kids under 2 years of age can now fly on an adult's lap at no additional charge on domestic flights, but the FAA says that's not the safest place for children to be on planes.
"Travel would be safer if the kid was in a seat. The U.S. government is thinking of requiring this, but if they don't, maybe the airlines will encourage this" by implementing a fee, Hobica said.
Ryanair charges 20 euros (about $26) each way for any infant traveling on an adult's lap.
But U.S. airlines know they would severely upset many travelers if they implemented a similar fee, Parsons said. Unless all of them decided to act at one time, it would be a risky move for any carrier who tries it first.
"If one airline decides to do it and they all don't match very quickly, that will steer business away from (that one airline) in a New York minute," he said.
In-person check in fee
This is the most likely fee to be implemented by at least one airline in the near future, Hobica said.
Most travelers already print their boarding passes at home and some prepay checked bag fees online as well. If you drop off your luggage at a conveyor belt at the airport and scan your own boarding pass at the gate, there's little need for any human interaction -- unless something goes wrong. Need to speak with an airline employee? There might be a fee for that.
"The airlines could save a huge amount of money by eliminating the ground staff," Hobica said.
The CEO of Florida-based ultra low-cost carrier Spirit Airlines already floated such an idea last year.
Still, Parsons predicted it would likely result in a mess.
"What happens when your flights are canceled? You have to talk to a human so you going to tell me it's going to cost me $25 to go find out why my flight got canceled? I have a problem with that."
Credit card fee
Not that airlines want to deal with cash, but they may want to look for a way to recoup the merchant fees they pay to credit card companies, Hobica said. (Typically a few percent of each purchase price.)
Passengers using an airline-affiliated card to book tickets might be exempt from any fee, he said.
British Airways already charges 4.50 pounds (about $7) for bookings made within the United Kingdom using a credit card. Booking by debit card is free.
Meanwhile, Ryanair charges an "administration fee" of 5 euros (about $6.50) per each flight that's booked by any method other than a specific company's debit card. Another European ultra low cost carrier, easyJet, has a similar policy.
Checked bag fees by weight or distance
Shipping companies charge more for heavier items and those being transported longer distances, so airlines might think about doing the same, Hobica said.
But Parsons said such a system would be too complicated for domestic carriers to implement, at least for the moment. He predicted airlines will stick with the system they have now: one fee for bags weighing up to 50 pounds, and another for heavier items.
Carry-on bag fee
Last year, Spirit Airlines became the first domestic airline to charge passengers to use the overhead space, a move that caused a huge uproar and prompted many travelers to worry that other airlines would follow suit.
"No one else has copied it yet, but Spirit Airlines is still flying and it doesn't seem to have hurt them," Hobica said.
Other airlines are watching the developments very closely, he said. Still, this is the least likely new fee to be implemented in the near future, Hobica said.
Major airlines have already said they don't intend to charge for carry ons, but that doesn't mean they won't do it sometime down the road, Parsons added.
"I'm still trying to figure out all the different places they can hit us -- they've hit us pretty good so far," he said.
Would you be willing to pay any of these fees? Let us know in the comments section below.