Or the airline could have sold major assets and discontinued flights on unprofitable routes.

You can book online directly with airlines or web-based companies selling flights; the following are good places to start:

But those problems have indirectly benefited several new companies that sell multiple flights on private jets.

The airline industry is rapidly dividing up into global alliances, which allow their members to jointly sell flights and share frequent-flier miles within the group.

Lastminute, a Web site that sells holidays and flights at short notice, went public in 2000, but has never made a profit.

These not only sell flights but also juggle capacities and fares in order to squeeze the last cent of revenue out of every aircraft seat.

Sunmaster Holidays has now sold flights, hotels and transfers to over 350,000 customers in total.

Last month Skyjet, which sold flights to India, became the 24th British travel company to cease trading this year.

In mid-October, British Airways was selling flights to Barbados from £649 return.

Think of it as the flip side of Virgin, which was selling flights before it tried to sell clothes.