A new twist on an old bet has taken sports betting in the United States by storm.

Same-game parlays, or SGPs, have emerged as not only one of the most popular bets on the board for bettors but also one of the most profitable for bookmakers.

In last year’s Super Bowl, 31% of bets placed before the game kicked off were same-game parlays at BetRivers, Barstool and other U.S. sportsbooks powered by Kambi, an international sports betting platform provider. At sportsbook PointsBet, 22% of all bets placed on the Super Bowl were SGPs. Both companies were anticipating even more Super Bowl SGPs this year. Not bad for something that sportsbooks in the U.S. only began accepting a few years ago.