Harrah's Winning Hand

"The reason why poker is important to a casino is that it brings traffic to the casino and players who end up playing other types of casino games, namely other table games," says Matthew Jacob, a gaming analyst with Majestic Research.

Harrah's paid $42.7 million in 2004 for the rights to the World Series of Poker brand and use of the Horseshoe brand in Nevada.

Besides the annual Vegas main event, the WSOP also hosts circuit tournaments throughout the country that boost Harrah's properties in South Lake Tahoe, Calif., Atlantic City, N.J., Mississippi and other markets.

While the WSOP is a big boost for Harrah's Rio casino in the summer, that property and other Harrah's poker rooms lag MGM Mirage's(MGM Quote) Bellagio casino for the rest of the year, according to data from Majestic Research.

Up until the World Series started, the Rio had only a 3% share of the Strip's poker usage. During the same period, the leading poker room was Bellagio, a perennial favorite, which captured 14% of the poker usage on the Strip. Next up were the Wynn(WYNN Quote) casino and another MGM property, the Mirage casino, which each captured about 11% of the poker action.

Caesars Palace, which Harrah's also owns, held 8% of the poker usage in that same time frame. Late last year, the property opened an expanded poker room, transforming it into one of the largest in the city.