Air Miles 'threaten dollar's dominance'

6m people in the UK have Air Miles

Air Miles currently in circulation are said to be worth $500 billion - making them the second biggest "currency" after the dollar.

Air Miles facts

American Airlines set up first airline reward scheme 21 years ago, called the "Advantage Travel Programme"

"Air Miles" originates from the UK 13 years ago

Name now franchised to third parties, including British Airways who has owned the UK Air Miles operation since 1994

Source: Air Miles UK

At its current rate of growth the stock of miles could overtake the dollar within two years.

The figures were calculated by the Economist, which reports that because there are so many unredeemed vouchers it will get harder for customers to secure the flights of their choice.

World currency

American Airlines was the first airline to launch a loyalty programme, called the "Advantage Travel Programme" 21 years ago.

Since then, some 100 million people around the world now belong to a frequent-flyer or loyalty scheme.

How many Air Miles do you need?

London to Paris (return): 450

London to Geneva (return): 950

New York (return): 6,800

Almost 50% of miles are earned without leaving the ground, as airlines sell miles to partners like credit card companies, telephone companies, car rental agencies, hotels and supermarkets.

UK history

Many schemes worldwide have now branded their loyalty programmes under the Air Miles trademark, which originated in the UK.

The Air Miles UK day-to-day operation has been run by British Airways since 1994, although the trademark is owned by an other organisation.

Six million people are members of the scheme in the UK.