The global gaming entertainment industry is huge and rapidly expanding. While research on gambling purchases is extensive, few researchers investigate cross-national gambling behavior. In a bid to explore the regularities of gambling purchases, this study applied the Duplication of Purchase Law to gambling purchases across the USA, Australia, and Macao. The Duplication of Purchase Law stipulates the relationship between the duplicated purchases of two competitive or complementary brands and their market shares. Results indicate that the law applies well across time and nations; the duplications of games played are highly correlated to games’ penetration rates. Gaming businesses can use the law as benchmark to ascertain the accuracy of their game penetration rates, to measure differences or similarities between individual games, and to track changes in their market. In addition, regulators may use the law as benchmark to manage the availability of gaming.