Despite the recent proliferation of legal online gambling in the Unites States, offshore gambling sites still remain prevalent, causing various problems in the U.S. Although numerous law violations occur in this domain, prior research has reported limited information about offshore gambling, mostly focusing on offshore gamblers’ characteristics and motivations. Using routine activities theory, this study attempted to understand environmental and theoretical factors that affect the use of offshore sites by focusing on offshore gambling-generating contexts that involve offshore sites and online casino reviews. Major findings show that the online visibility of offshore sites may be a key predictor of the use of the sites by U.S. players. In addition, online casino reviews providing a blacklist of online gambling sites served as informal guardians, helping players avoid unreliable offshore gambling sites that pose a risk to their customers. Policy implications were suggested based on the findings and provided insights toward effective online gambling regulatory efforts.