In apparatus (10), a progressive jackpot is awarded in the event that the outcome of an actual series of games at gaming locations (12,13,14) is the same as the outcome of a hypothetical series of games. The hypothetical game outputs are determined by a random number of generator (21) and a plurality of jackpots of differing values may be won depending on the number of games in the hypothetical series. The jackpot amount is incrementally increased for each game played which does not result in a jackpot win and is reduced to an initial value after a jackpot win.