US Patent 7604540 Linked progressive jackpot system

A gaming machine 10 has a display 14 and a game controller arranged to control images of symbols displayed on the display 14. The game controller is arranged to play a game 16 in which at least one random event is caused to be displayed on the display 14. If a predefined winning event occurs, the machine 10 awards a prize to a player. When a trigger condition occurs in a base game of the game 16, a bonus game feature is awarded comprising a series of bonus games. If a particular special symbol outcome occurs during any of the bonus games, the particular special symbol outcome is collected towards a jackpot prize awarding event.