Why one extra pocket changes the odds
On an American roulette wheel, a straight-up bet on one number wins only if the ball lands in that exact pocket. The wheel has 38 pockets: numbers 1 through 36, plus 0 and 00. A single-zero wheel has 37. The extra pocket makes every individual number slightly less likely to hit, while the usual payout stays the same.
The payout does not keep pace
A $1 straight-up bet pays $35 in profit if it wins, and the player gets the original dollar back. On a 38-pocket wheel, the chance of winning is 1 in 38. A fair payout for those odds would be $37 in profit; paying $35 leaves the casino with an advantage.
If a player made the same bet many times, the average loss would be about 5.3 cents per dollar wagered on the American wheel. On a 37-pocket single-zero wheel, it would be about 2.7 cents. These are long-run averages, not predictions of what will happen in any short session.
The green pockets affect more than number bets
The 0 and 00 are not part of the red/black or odd/even groups. When the ball lands on either, those even-money bets generally lose too. The added pocket therefore gives the casino another outcome that defeats many common wagers, not just bets on individual numbers.
That small change is why the two wheels can look nearly identical yet offer meaningfully different odds: the American wheel adds a losing possibility without adding a matching increase to the payout.
