The upcoming superfight between Floyd Mayweather and Conor McGregor has been dominating headlines since it was announced in June. It’s drawn in fans from all walks of life, from hardcore viewers of combat sports, to casual observers who haven’t watched more than a few matches over the years, to people who have never even watched a fight. As sportsbooks around the world have quickly figured out, a lot of these people are also quite interested in betting the outcome.

McGregor is far and away the fan favorite, and the underdog is generating a flurry of tickets backing him to win. According to ESPN, the UFC star is responsible for 95% of bets at William Hill’s Nevada book, and MGM writes just one Mayweather wager for every 27 it doles out on McGregor.

These are staggering figures, especially considering it is McGregor’s first professional boxing match — and against arguably the greatest pound-for-pound boxer of all time, with an unblemished 49-0 record. Should McGregor pull off the stunning upset, the sportsbooks will be on the hook for massive losses. William Hill admitted that liability is now “well over” a million dollars for a McGregor victory and is hoping—along with just about every other bookmaker on earth—that a flood of late money pours in on Mayweather.