To understand some of the deviations from recommended optimal play in Blackjack, gamblers were considered to be decision makers who used decision rules to predict outcomes. The size of their wagers were used as an index of the confidence of these predictions. If this were the case, players' decisions would be affected by time pressure, short-term probability of winning, and their perceived control of outcomes. Players' wagering on a simulated game of Blackjack was examined to assess the feasibility of this approach. The computer simulation of Blackjack used simplified rules (no splitting, doubling down, insurance, etc.), and the probability of winning was controlled by the computer. Subjects could either choose whether they were dealt extra cards, or could bet upon “another player.” The “other player” was a computer algorithm that sat upon a total of fifteen. To examine effects of time pressure upon confidence of judgments, the time allowed to place a bet, and to choose extra cards, was manipulated. Twelve subjects played 20 hands under each of the experimental conditions. The mean amounts wagered, and players' choice of cards were both examined. The results suggested that deviations from optimal play can in part be understood in terms of players' decision processes, that are influenced by the time available to make a decision, the short-term probability of winning, and perceived control of outcomes; each factor may potentiate the effects of the others.