In the past six months, it has twice put up some domestic and excess bag charges - by as much as $50 apiece - in response to increased operating costs.

The IdeaWorks report finds that when ranked as a percentage of total revenue, low-cost carriers dominate.

Florida-based Spirit makes 46.6 per cent from ancillary charges, Mexico's VivaAeroBus 43.6 per cent, Denver-based Frontier 42.4 per cent and fast-growing Hungarian airline, Wizz Air on 41.6 per cent.

The report says 50 per cent seems to be the ceiling for ancillary revenue, noting Ryanair boss had often remarked fares some day could be zero.

''Over time that objective eluded Ryanair, with other airlines doing much better.''

Low-cost carriers had become ''low-fare champions'', competing with bus services in some countries and providing an economical lifeline for many workers in Western Europe to travel to former Eastern Bloc countries.