Combo bet is a bet consisting of two or more unrelated elections on the betting exchange, for winning which every selection must win or it needs to be a return (flow).
The odds of the combination of the "Express" bet is equal to the product of the odds of all constituent elections. Potential winnings on an express, is equal to the product of bet amount and the odds of express. If on any selection in the express occurs a return flow), this choice receives odds of 1.0 to calculate express. This is possible, for example, if the express includes handicap (0) in a football match that ends in a draw. The potential profit of express the greater, the more choices it includes and the higher the odds, but the degree of risk also grows along with the increase of the number of events in the express.
The minimum possible number of selections in the express is usually two. The maximum possible number of choices and/or a maximum possible odds of the express is determined by each bookmaker individually. For example, at the betting exchange Betfair these are 8 events, whereas in bookmaker office "the Marathon" — 20. In "Pari-Match" odds can not be more than 2000,0, and at "the Marathon" — 1000,0.
Professional betters prefer no to bet the type of "express", because the increasing number of elections increases the advantage that a bookmaker holds over the player.