Of Course, every time when you lose, you need to double your investment. In theory it sounds easy, but when you start play it's not. After every investment you can lose.

For example:
invest:
1 - lose
2 - lose
4 - lose
8 - lose
16 - lose
32 - lose
64 - lose
128 - lose

and so on

I'm playing on k8poker and for now it seems ok. But you can play only poker, roulette and slots :/

I tried Martingale System and I can say with certainty that Martingale almost allways fail. The main reason is that you need a huge amount of money.