A method of operating of controller-based progressive gaming system having a plurality of gaming machines wherein each gaming machine generates unit bet information indicative of a number of unit bets supplied to a machine for playing a game. The method comprises the steps of randomly selecting a bonus mode activation value between a high and low limit, providing a current value, providing a base value, incrementing the current value when the gaming machines are played so that the current value is incremented by a fixed amount of each unit bet received by each gaming machine. A bonus mode time period is entered when the incremented current value is equal to or exceeds the bonus value. Eligible machines are locked-in and random bonus jackpots are made during the bonus time period. Each bonus award decrements the current value by the amount of each award and the bonus mode time period is ended when the current value is less than or equal to the base value.