En Prison Rule

The en prison rule is a special provision in European roulette that applies to even-money bets (red/black, odd/even, high/low) when the ball lands on zero. Instead of losing the entire bet, the wager is imprisoned, held in place for the next spin. If the next spin produces a winning outcome for the imprisoned bet, the original wager is returned without profit.

The en prison rule effectively cuts the house edge on even-money bets in half, from 2.70% to 1.35%. Without the rule, you lose your entire bet on zero. With the rule, you get a second chance, and the expected value of the imprisoned bet is exactly half your original wager. This makes en prison roulette one of the best bets in any casino.

Some versions of the en prison rule have additional provisions. If the ball lands on zero while a bet is already imprisoned, the bet may be double-imprisoned (requiring two consecutive wins to be returned) or lost entirely, depending on the house rules. The double-imprison variant maintains the 1.35% house edge while the lose-on-double-zero variant slightly increases it.

The en prison rule is most commonly found in French roulette and in some European roulette games at upscale or traditional casinos. It is relatively rare in North American casinos, though some high-limit rooms offer it. Online casinos often feature French roulette with la partage or en prison. When available, always choose a table with this rule for even-money bets.