Low cost airlines are notorious for their add-ons; food and checked-in baggage cost extra on many Australian flights.

Now no-frills airlines overseas are going even further. Ireland's Ryanair has confirmed it plans to charge customers to use the toilets and an American low-cost carrier wants to charge people to use overhead lockers if their bags do not fit under the seats in front of them.

It may seem outrageous to some but analysts say there is a good reason airlines might start to charge for using overhead lockers or toilets.

Centre for Asia Pacific Aviation chairman Peter Harbison says wafer thin margins are behind the moves.

"First of all they can get an extra half-a-dozen seats in, which is more than the profit usually for a whole aircraft operation," he said.

"It saves them a lot of money in servicing two additional toilets. All those sorts of issues, they all add up quite considerably."

Mr Harbison says it is quite possible that Australian carriers will also consider following suit at some point in the future.

"I've got no doubt that every airline is looking at how much space the toilets take up, and not just low cost carriers but all carriers," he said.

"And bear in mind too that we're not talking about six, seven, eight-hour flights here. We're talking about 45 minutes to an hour, so it's not something that's likely to strain the ability of most people for that length of time."

Ellis Taylor, a reporter for Australian Aviation Magazine and former Jetstar employee, says Ryanair's move is a bold one and Australian airlines are likely to be cautious about doing the same.

"At this stage I think they'd be very bold. I think a lot of people are going to wait and see how it goes down with Ryanair first," he said.

"I'm not aware of the airlines in this part of the world looking at that option and I think a lot would argue that it actually probably goes a little bit too far.

"But you know in this day and age you never know what will happen."

Mr Taylor says the process of separating charges is likely to continue as airlines attempt to improve their profit margins.

But he says there are a number of potential complications, including the role of flight attendants.

"Essentially they're going from people who are concerned with safety and service into, for lack of a better word, checkout chicks; just looking to collect revenues be that through credit cards or cash and so forth," Mr Taylor said.

"And I think there's going to be some resistance from flight attendants because to some of them it might be cheapening their role."

Virgin Blue says it currently has no plans to charge for either toilets or overhead lockers.