This paper considers the cardgame Blackjack according to the rules of Holland Casino's in the Netherlands. Expected gains of strategies are derived with simulation and also with analytic tools. New effiency concepts based on the gains of the basic and the optimal strategy are introduced. A general method for approximating expected gains for strategies based on card counting systems is developed. In particular it is shown how Thorp's Ten Count system and the High Low system should be used in order to get positive expected gains. This implies that in Holland Casino's it is possible to beat the dealer in practice.