Supercross is a motorcycle-based sport that involves high performance motorcycle races over dirt tracks. Similar to Motocross, Supercross events are usually conducted inside a stadium, but can also take place outdoors. The main difference between the two forms of racing is that there are more jumps in Supercross, while in Motocross riders do not take to the air as much. This sport is very popular in the U.S. where the "outdoor" (ie Motocross) stars do both Motocross and Supercross. Supercross does not enjoy the same popularity in Europe however, as European Motocross stars do not normally compete in European Supercross events. The advent of a world championship incorporating most of the American championship, and a few races in Europe, may change this.