A study by Juniper Research claimed that while platforms like Twitch, which use a subscription model, would contibute some part of these revenues, the major share of income will be from advertising.
Almost 90% of eSports and Let's Play viewers would be watching ad-supported casual games streams four years from now, Juniper predicted.
The research firm said that commentary on streams of the playing of video games, known as Let's Play, had grown in popularity.
Juniper put forward the argument that companies which wanted to make money off this trend should join hands with a streamer who shared their values or else follow closely content that was publicly published.
Research author Lauren Foye explained: “As we saw following PewDiePie’s recent controversial videos, a breach of a sponsor’s values can result in the termination of lucrative partnerships.
"Nevertheless, a rise in PewDiePie’s channel engagement following the scandal highlights a quandary sponsors are facing.”
She added: "Whilst advertising, and increasingly tips, are dominant in the viewership of casual games streaming, eSports content has begun to be monetised through alternative means.
"Juniper believes that the sale of merchandise, time-limited content (such as in-game items), and access passes, will form part of a wider trend to drive the industry forwards. As we saw with DOTA 2’s 2016 ‘The International’ tournament, sales of additional content boosted the prize pool by US$18 million."
The study, titled eSports, "Let’s Play & Watch Play: Competitive Tournaments & Content Streaming 2017-2021", can be downloaded from Juniper's website.