The Martingale System
The basis of the Martingale system is the idea that eventually in online roulette, the player should hit a win every roulette tournaments. Since there are only a limited number of potential spaces for the ball to land in, at some point the player will be able to make back any losses with a win. In order to make such a strategy possible, the player must bet on the same number and with each loss double the bet. When the win finally comes along, the player is going to get the payout he or she would have gotten if every ball had been a win.
The Drawbacks of the System
Though the Martingale system is one of the most popular online roulette betting systems, it does have its limitations with casino roulette variant. One of these comes into play when the doubled bets bump up against the betting limits at the table. If the player hits the betting limit before he or she has recouped the losses, then it is unlikely the player will ever fully recoup those losses. There's also the chance that due to the random nature of roulette, the player may not win for a very long time and may run out of money before reclaiming the losses.
Even the most effective online roulette betting systems can be ineffective when the player is decidedly unlucky. The game is always random, and no betting system can make up for that.