DANIEL NEGREANU IS one of the most successful poker players in the world, the winner of six World Series of Poker championships who has racked up more than $19 million from live tournament pots. So sharp is his bluffing that he once went on a TV science show to try to fool a lie detector—and, ultimately, he succeeded.

But until recently, the 39-year-old star put some serious resources into a strategy that most fans know little about. He hedged his bets, by investing in other poker players. Two years ago, he says, he invested about $2 million in 10 players at the World Series of Poker, and at times he has played against some of those he has backed in tournaments. "I play against them as hard as I play against someone I don't even know," he says.

To most observers, professional poker is a straightforward game of winners and losers, with almost $200 million in prize money dished out at more than 60 World Series of Poker events last year alone. With cameras that reveal each player's cards, devoted fans can see how every hand is played and the strategy behind each bet. But there's one thing they can't see: the financial dealing among the players.

Whether it's played face-to-face among steely-eyed pros, or online where each person may be participating in many games at once, professional poker has developed its own economy. That economy is based on players not only betting with their own money but also getting "staked," or financially backed by former and current players. Many players also agree to invest in each other and swap a small part of their earnings.

Such deal-making isn't new to the game, but veteran players and analysts agree that the amount of money—and level of sophistication—involved in the arrangements has risen considerably since the World Series of Poker championship began in 1970. According to players, agents and other experts in poker interviewed by WSJ.Money, at least half of the estimated 6,600 contestants in this summer's Main Event championship in Las Vegas, the game's biggest annual competition, are likely to receive financial support from past and current players, family members and other poker investors. The event last year collected $64 million in entry fees, which means the backing could've been in the vicinity of $30 million.