For sports gamblers, this Saturday will be like Christmas come early. Between the Kentucky Derby in the afternoon and the Mayweather—Pacquiao fight that evening, hundreds of millions of dollars will be wagered across the country.

In Nevada, the welterweight match between Floyd Mayweather and Manny Pacquiao could generate upwards of $50 million in bets, which would be a Nevada record.

Michael Grodsky is director of marketing for William Hill U.S., which operates more than 100 sports books in that state. He says, “80 percent of the bets that have been made are on Manny Pacquiao, and that’s also 65 percent of the money that’s in bet. So, we’ll be rooting for Floyd Mayweather.”

The Kentucky Derby also stands a chance of breaking betting records, but if you want to bet legally on other sports this weekend, Vegas is king.

Johnny Avello is known as the “Wizard of Odds” on the Vegas strip. His official title: executive director of race and sports operations at the Wynn Las Vegas.

“Well, if you like horse racing, boxing, NBA, NHL and baseball … I guess it’s a gambler’s delight,” Avello says.

However, it’s still just a drop in the bucket in terms of total betting. “I always estimate that Nevada’s probably 3-4 percent of everything that’s wagered in the U.S.”

Outside of horse racing, which is legal in other states, Avello says most sports betting in the U.S. is underground.