A gaming system includes a credit mechanism configured to receive credit input by a player for contribution to a credit balance and a display configured to display a plurality of standard symbol positions and optionally one or more additional symbol positions. The system also includes a betting module configured to determine a bet amount and game play instructions on commencement of a game input using a player interface, the bet subtracted from the credit balance. A symbol selector selects symbols for display in the plurality of standard symbol positions and, dependent on the amount wagered, further arranged to select and display symbols in the additional symbol position(s) to increase the probability of a win outcome being generated. An outcome determiner determines an outcome of the game based on the displayed symbol positions.