The “En Prison” rule only applies to European roulette, meaning gamblers playing the American version and other game variants cannot take advantage of it. Also called the “in prison” rule, it gives players betting on even money bet an extra spin if the marble-sized ball lands in the “0” pocket.
If the said probability occurred, as the rule’s name suggests, the dealer puts a marker on the bet, indicating its imprisonment, for the next spin. Once the gambler wins the next spin, he gets his original bet back. With this rule coming into play, it can further reduce the house edge to 1.35%. However, if the player bets $100 on even and an odd comes after the zero instead, he loses his stake.