Gambling both online and offline is called mixed-mode gambling (MMG). This study compared people who gambled online only (ONGs), people who gambled offline only (OFGs), and people who gambled in mixed modes (MMGs) in terms of gambling involvement and severity. It also compared the three subgroups in terms of motives for gambling and personality traits. A total of 517 adults who lived in the United States participated in this study. All participants had moderate-risk or problem gambling based on the Problem Gambling Severity Index (PGSI) and had gambled in the previous six months. The results showed that MMGs engaged in a wider range of gambling types than ONGs and OFGs. MMGs also had more severe problem gambling than OFGs and ONGs. MMGs were more likely to gamble to enhance positive feelings and for socialization than OFGs and ONGs.