All casinos have a mathematical advantage and should always win over time. Individual players may win but the greater the overall volume of betting the better the chances for the online casino. People are always coming up with systems and strategies that they believe will give the edge that they are looking for. Over the long run no betting system will allow you to beat the casino. The house has too great an edge and compensates for weaknesses. If someone did come up with a true working system no one else would find out about it. There are some online gambling systems that are widely used and they do have some validity as far as extending your bankroll. This is true for both land based and online casinos. The most widely recognized of these strategies is the Martingale betting system.
The doubling strategy or Martingale system is a popular system. It is sometimes known as a reverse regression or loser's strategy. This system is played in even money games such as roulette or blackjack where the player doubles his money when he wins. In these systems a gambler doubles his bet after each loss. With this strategy a win would erase the losses of all previous games plus win the gambler back his original stake. Since a gambler with infinite money would eventually win this system is sometimes thought of as a sure thing. Over time this system will in fact bankrupt the gambler because no gambler possesses infinite wealth and the bets grow exponentially. Extended losing streaks will quickly wipe away all profits. After the sixth consecutive loss the gambler would need to bet 128 times his original stake or $640 in order to win back his previous bets on a five dollar original bet. It is thought that betting limits at tables are used to control this system. These limits are actually in place to protect the casino from large losses on a hot run.
Use roulette as an even money game. In roulette if you are betting only red or black, you will win 46% of the time. You will lose 54% of the time. The idea of the Martingale system is to overcome these odds. If you were betting just black or red you would eventually lose all of your money. Consistently doubling your bets will effectively wipe out several of these losses and move the odds into your favor. There is just a 10% chance of losing 3 rolls out of three. This would translate into losing three in a row. There is only a 1% chance of losing six out of six. This all makes sense as long as you don't hit that long run of losses.
No system will work over a long period of time. The cancellation betting system is also known as the Alembert system. It is a more complicated betting system that works as long as you win and lose the same amount of times in even money game. You will not win a lot using this system but you will play for a long time.