Are some wagers at double-zero roulette better than their single-zero counterparts?
Answer: In "American" or "double-zero" roulette, the ball can land in one of 38 grooves. In "European" or "single-zero" roulette the ball can land in one of 37 grooves. This means there's a slightly greater chance to lose bets on double- rather than single-zero layouts. Payoffs on hits are the same in either game, so casinos have more edge on American wheels – and offer the European version to high rollers in exchange for larger bets.
Here's another way to view the difference. Betting $1 on every position in the double-zero game, you'd win $35 on the one spot that hit and lose $37 on the 37 that didn't – a net loss of $2. Betting $1 on every position in the single-zero game, you'd win $35 and lose $36 – net loss is cut in half, to $1.
An exception occurs in some casinos on "outside" or "even-money" wagers – red, black, odd, even, 1-18, or 19-36. These pay 1-to-1 when they win. On double-zero wheels, they lose completely when opposing numbers from 1 to 36 hit – for instance, you bet on odd and the ball lands on 14; however, in Atlantic City and occasionally elsewhere, they only lose half when the ball stops in 0 or 00. On single-zero wheels, these bets lose completely when the ball lands on 0 as well as on opposing numbers. For these wagers, the 50 percent recovery on green in the American game cancels the penalty otherwise inherent in the extra position.
There’s also the en prison rule that was popular at one time in Europe but rarely encountered today. On even-money bets, when the ball lands in 0 or 00, the player could either take back half the wager or leave it on the table for another spin. Two greens in a row was a loss but the second spin was otherwise treated like a new bet. This rule, like the automatic half bet return, cuts house advantage in half.