In European roulette there’s a single zero after which the numbers 1 – 36, however in American roulette there is a single zero and a double zero and numbers 1 – 36. The additional digit in American roulette implies that when you place your chips on a single number you have one probability in 38 of getting the desired end result, whereas in European roulette you’ll have one probability in 37. It may not sound like a huge distinction but it significantly impacts the house edge.