In the United States, almost all gamblers use the American odds format, whereas Decimal odds are far more prevalent in the United Kingdom for example. It can also vary by sport where conventions have created the norm. Sportsbooks will often display odds for Horse racing with fractional odds for example, and MMA markets using American odds even if that isn't the most popular format for the region as a whole. Most sportsbooks will default to the preferred odds format of their audience by using rules mapped to IP detection. Any worthy sportsbooks will also offer users the ability to override that default format to their own preference.