Some French tables will employ rules that generally help out the players. The "La Partage" and "En Prison" rules apply to outside even money bets like odds or even, black or red and low or high; they also apply when the ball lands in the zero slot. They are similar in the sense that players only lose half of their bet, but players cannot leave their bet on the table for another spin with the La Partage rule. If a player loses, they can collect half their bet in the En Prison rule, or leave half their bet on the table for the next spin with the La Partage rule.
On an American wheel, there are 38 spots: numbers 1-36, plus 0 and 00. Your odds of winning a one-number bet are 37 to 1 (37 ways to lose, 1 way to win). But if you win, the casino doesn't pay you 37 to 1, they pay you less: 35 to 1. The difference between the true odds and what they actually pay you is 2/38, or 5.26%. You can do this same calculation for the other bets, and it comes out the same.