Its impossible to make a betting system that will be 100% successfull, and the reason is because you dont get paid the real odds according to what you bet on.

For example, to get 1 number come up in roulette pays 36/1... The real odds are 37/1. In American Roulette its even worse... 38/1. Avoid American Roulette like the plague.

Like mentioned before the only "system" is card counting or tracking. You cant do this online though, as theres no shoe to track or count from.