bet exchange

The concept was first brought to the public by the UK website Flutter.com in May 2000 in person-to-person betting form, followed closely by UK-based Betfair in June 2000. Betfair embraced a pure exchange model - one Flutter later adopted and, some say, even improved upon in places - but first-mover advantage proved decisive for Betfair. Though Flutter managed to climb to a reported 30% market share, Flutter's backers were content to broker a merger which left Betfair the dominant partner by a reported ratio of 84:16. Post merger, Flutter's customers were transferred to Betfair's system, which was later upgraded to embrace some of Flutter's functionality. Betfair went from strength to strength and controls a reported 90% of global exchange activity today. In late 2004, Betfair announced a rescue package which resulted in it absorbing the customers of Sporting Options, which had gone into administration with debts in excess of £5 million.
As with other types of exchanges, betting exchanges thrive on liquidity and customers tend to focus on the exchange where they are confident their bet can be paired up with a matching counterbet. Breaking with British tradition, Betfair uses decimal odds instead of fractional (traditional) odds because they are more popular globally. Some of its competitors allow customers to use fractional odds if they prefer.
Most exchanges make their money by charging a commission which is calculated as a percentage of net winnings for each customer on each event, or market. Gamblers whose betting activities have traditionally been restricted by bookmakers (normally for winning too much money) have found these sites a boon since they are now able to place bets of a size unrestricted by the exchange - the only restriction is that one or more opposing customers need to be willing to match their bets. Moreover, the odds available on a betting exchange are usually better than those offered by bookmakers, in spite of the commission charged, because the middle man is eliminated.
Exchanges currently have some limitations. Exchanges are not currently suited to unrestricted multiple parlay betting. Betfair does offer accumulators but these are limited in number and type: Users cannot determine the outcomes contained in accumulators themselves. Exchanges also tend to restrict the odds that can be offered to between 1.01 (100 to 1 on i.e. 1 to 100) and 1000 (999 to 1).
Unsurprisingly, Betfair's success has attracted a number of rivals.
Exchanges also offer the opportunity to lay, which is to bet that a selection will lose. This is the position bookmakers have traditionally taken when offering a bet to somebody to back that the outcome will win.
For example, if someone thinks Team A will win a competition, he may wish to back that selection. A bookmaker offering the punter that bet would be laying that selection. The two parties will agree the backer's stake and the odds. If the team loses, the layer/bookmaker keeps the backer's stake. If the team wins, the layer will pay the backer the winnings based on the odds agreed.
As every bet transacted requires a backer and a layer, and the betting exchange is not a party to the bets transacted on it, any betting exchange requires both backers and layers. Of course, the distinction is moot: A layer is always simply backing the opposite outcome. Laying the home team is the same as backing the visiting team to win or draw. Laying one horse in a race is just the same as backing all of the other horses to win