Roulette: when double-zero beats single-zero

Nearly all bets at double-zero roulette wheels give the house a 5.26% edge, the exception being the five-number-bet on 0, 00, 1, 2 and 3. That one bucks a house edge of 7.89%.

All bets at single-zero roulette wheels have a house edge of 2.7%. There is no 00 to worry about, and no five-number bet with a higher house edge than the rest.

If all else was equal, choosing between single-zero and double-zero roulette would be a no-brainer. The house edge on the double-zero game is almost double that on the single-zero version. But there are complicating factors. First and foremost is that single-zero roulette is not common in the United States. Most tables have the double-zero. And casinos that offer single-zero roulette usually put higher minimum bets on the lower house-edge game.

Should a player on a $5 a spin budget go to a $25 minimum wheel just because it has the lower house edge? No, staying within your bankroll and not betting money you can't afford to lose is rule No. 1 for anyone with a limited casino entertainment budget.

But there are circumstances in which the better play is to go to a double-zero wheel, even when the house edge is the only consideration. It happens when bets that pay even money at a double-zero wheel take only half your bet when the ball lands in 0 or 00. That lowers the house edge to 2.63%, provided you stick to the even-money bets -- red or black, odd or even, first 18 or second 18. Other bets still carry the full 5.26% edge, and it's still a whopping 7.89 on the five-number.

It's a rule seen most often in Atlantic City, a rare variation in the rest of the country. Casinos that offer it tend to restrict it to double-zero tables. If you move to a single-zero wheel, you're still facing a house edge of 2.7% on the even-money bets, making the double-zero version an ever-so-slightly better play.

Here's the way the reduced house edge works. Imagine a sequence in which you bet $10 on black each of 38 spins, and the ball lands in each number once. You risk a total of $380. On each of the 18 black numbers, you keep your $10 wager and get $10 in winnings, meaning you have a total of $360.

If that's all there was to it, the house would keep $20. Divide that $20 by your $380 risk, then multiply by 100 to convert to percent, and you get the 5.26% house edge that's standard on double-zero roulette.

But since the house takes only half your bet when the ball lands in the zeroes, you still have $5 of your $10 wager after the ball falls in 0, and another $5 on the double zero. That means at the end of the trial, you have $370, and the house has only $10. Divide $10 by $380, then convert to percent, and the house edge is cut in half, to 2.63%.

It's a cousin of the European "en prison" rule, used on single-zero tables overseas and on a few high-limit tables in Las Vegas. Instead of losing on 0, your even-money bet is held imprisoned for an extra spin, and you have a chance to win it back. That lowers the house edge to 1.38% on a single-zero wheel.

This one also is restricted to bets with even-money payoffs such as red or black, odd or even or first 18 and second 18. If you want to bet the single numbers or combinations of numbers on the inside, or on the columns, dozens or other options, you'll still face the full 2.7% house edge of single-zero roulette.

Let's say you bet on black, and the ball lands on 0. Your bet is held en prison. If the next spin brings a black number, you get your bet back. There are no winnings to go with it, but at least you get your money back. But if the spin after the 0 is red or another 0, then the casino takes your bet.

There are variations. There's a double imprisonment rule, where if the spin after a zero is another zero, you don't lose immediately. Your bet is just moved to another prison level. If you've bet on black and two zeroes follow, it takes two black numbers in a row to get your bet back. With that second prison level, the house edge drops a tiny bit more, to 1.37%.

The half-loss on the zeroes version can't drop the house edge quite that low since we see it on double-zero games. But it can make roulette easier on your bankroll.