We may grumble about having to fork out extra to check-in your luggage or watch movies in-flight – but when you realise what's in it for airlines, you can see why they do it.

The 2011 combined ancillary revenue for 50 of the world's airlines was US$22.6 billion, according to a report released this week.

The Amadeus Review of Ancillary Revenue Results says that is a 66 percent jump on the reported revenue from 47 airlines in 2009, msnbc.com reports.

Compared to last year's statistics though, it's just a 5.3 percent rise.

Ancillary revenue is all the non-ticket charges – like priority boarding, checked bags, food, drinks, as well as income earned through branding partnerships.

The top five earners last year were:

• United Continental: $5.2 billion
• Delta: $2.5 billion
• American: $2.1 billion
• Qantas: $1.4 billion

• Southwest: $1.2 billion

Some of the more unusual optional extras include Qantas's Q Bag Tag, which allows travellers to skip the lines at the counter for AUD$50.

Spanish airline Vueling will let you board early, give you a drink and snack and keep the middle seat empty for 60 euros.

IdeaWorks president Jay Sorensen helped produce the report and says the report looked at financial documents filed by 108 airlines, and tallied the ancillary revenues for the 50 that provided the figures .

"Among the top producers, the growth is slowing because they’re reaching the limit of what can be sold to a customer.

"But worldwide, it's going to keep growing because there are so many carriers that are still not doing the bare minimum."

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