At step 40 the parameters for the jackpot are initialized, including a storage criterion and an award criterion. At step 41 the current value of the jackpot prize pool is calculated. At step 42 the CPU 2 checks whether the storage criterion has been met. If so, the currently accumulated value of the jackpot prize pool is stored at step 43 in memory 6 as a pending jackpot, along with the award criterion that is associated with that pending jackpot. The jackpot parameters are then redefined and the accumulation of as new jackpot prize pool is ready to commence. A number of pending jackpots may be concurrently stored in memory 6, each with an associated stored award criterion. At step 46 the CPU 2 determines if any of the award criterions that are associated with the pending jackpots have been met and if so, the associated pending jackpot prize is awarded at step 47 in accordance with a jackpot prize distribution scheme.