Martingale is definitely one of the most widely known and most successful roulette strategies (for some it is the best roulette strategy), and it is very simple to apply. It can be used only for outside bets, those that provide almost 50% chance of winning, and excluding the 0.
What are the best odds in roulette? The bets with the best odds in roulette are outside bets on either even or odd, red or black or numbers 1-18 or 19-36. Each of these bets has a 1:1 payout.