Fixed-odds gambling

Fixed-odds gambling is a form of gambling against odds offered by a bookmaker, an individual, or on a bet exchange. It is customary with fixed-odds gambling to know the expected odds at the time of the placement of the wager (the "live price"), however this category also accommodates wagers whose price is determined only after the race has taken place (the "starting price"). It is typical for a bookmaker to price up a book such that the net outcome will always be in his favour, i.e. the sum of all possible outcomes will be in excess of 100%. The amount of the sums wagered in excess of 100% represent profit to the bookmaker in the event of a balanced book. This excess is known commonly as an overround.

With the advent of internet and bet exchange betting, the possibility of fixed-odds arbitrage actions and Dutch books against bookmakers and exchanges has opened up significantly.