Common roulette wheels have two sets of eighteen numbers, one coloured red and the other black. There are also one or two green zeros, depending on the variant being played. Every game offers the option to bet on single numbers, groups of numbers, colour or the sets of even and odd numbers.
European roulette is locally the most common variant of the game. Along with numbers from one to 36, it has one green zero. Therefore, the probability of the ball landing on zero is one in 37 (2.7%), making it statistically profitable for a casino with every spin.
French roulette is more player-friendly. It has one zero like European roulette, but when the ball lands on on the zero players are returned half of their bets, in a rule known as "la partage." Therefore, the theoretical profit for the casino over every spin drops to half the rate of European roulette, namely 1.35%.
In addition to the standard zero discussed above, American roulette contains a second zero. The probability of hitting zero or 00 is therefore two in 38, or 5.26%. Furthermore, the layout of numbers on the wheel differs from the other variants.