In the UK and Ireland 2-team parlays are known as doubles, and 3-team parlays are known as trebles. Parlays offer a bettor a greater possible return for greater risk. If any of the underlying bets lose, the entire parlay is graded as a loss (if an underlying bet pushes then the parlay is treated as if the pushed leg never existed – so a 4-team parlay would become a 3-team, a 3-team a 2-team, and a 2-team a single bet). Each of the underlying bets must win for the parlay to win.

A parlay (often referred to as an accumulator in the UK) is a single bet whose outcome is determined by two or more underlying bets.