The purpose of the present investigation was to test the skill/luck distinction among gambling games by comparing the motivations underlying participation in a skill (horse racing) and a luck (lottery) betting activity. Predictions were made using Self-Determination Theory (Deci & Ryan, 1985, 1991). It was predicted that self-determined motivations (intrinsic motivation and identified regulation) would be more prominent for the skill game because it is conducive to optimal challenges, fun, and self-involvement. Conversely, the non self-determined forms of motivation (especially external regulation) should be more important for the game of luck because the luck dimension precludes true involvement of the self and orients the individual towards material gains. Results from a hierarchical discriminant function analysis, with 120 gamblers predominantly involved in one of the two betting activities, supported these hypotheses. These results highlight the relevance of a motivational analysis for a better understanding of the inherent properties of gambling games.