Males aged between 21 and 35 watch eSports as often as they watch basketball or hockey.
This data comes from market intelligence firm Newzoo, which studied people's viewing habits of sports and compared them to eSports.
Its report found that 22% of male millennials watch eSports. 76% of these people also claim that their viewing of eSports is taking away time previously used to watch traditional sports.
Six million of the 20 million eSports fans do not watch any other kind of sport. 40% of all eSports fans don't even play the games that they watch.
Room to grow
"If eSports would generate as much revenues per fan as the NBA, it would be a $2.5 billion business today," says Newzoo in its report.
The study also found that 39% of eSports enthusiasts have played Supercell's Clash Royale in the last three months, compared to 17% of all gamers.
Newzoo has previously predicted that one billion people around the world will be "aware" of eSports by the end of 2016.