Before moving to America and the "New World" this game was called "European Roulette" or "Zero Roulette" in France where it was invented. In North America was adapted
and it plays off of a wheel with both a zero pocket, and a double zero pocket.
The House Edge suffers a direct effect with the addition of a second green 'zero' pocket on American roulette. For the European roulette you can use the following formula, and you can find that the house edge is also a consistent number across bets, but the number is much more player-friendly.
The American roulette has in total 38 numbers, 2 being green pockets that cannot win on outside bets. By the following formula the expectancy of this game is -5.25%:
E = [1/38 X 35] + [37/38 X -1]
= [0.921] + [-0.9736]
= -0.526 or -5.26%
The European roulette wheel has in total 37 numbers, with 1 green pocket that cannot win on outside bets. By the following formula the expectancy of this game is -2.70%:
E = [1/37 X 35] + [36/37 X -1]
= [0.945945] + [-0.972972]
= -0.027 or -2.70%
The house edge of European roulette it doesn't reach the half from American roulette. Any gambler will say, a house edge of 5.25% is horrible, but a house edge of 2.70% is very reasonable.