Gaming intelligence group SuperData has released a new report on the digital card game market, noting that it expects this segment to earn $1.5 billion in 2018 and that this should increase to $2 billion by 2020.

Hearthstone remains the most popular digital card game in the U.S.. The North American digital card game market will earn $414 million in revenue, accounting for 26.7 percent of global revenue. North America will have a total digital card game audience of 14 million people this year. And according to SuperData, 71 percent of digital card game players use their smartphones. PC is next with 47 percent, then tablets with 44 percent. Consoles are in last with 26 percent (Hearthstone is not available on consoles). Three out of four players have spent $10 or more on additional content.

Blizzard launched Hearthstone in 2014, and it helped start the digital card game explosion. While it has competitors with games like The Elder Scrolls: Legends, Magic: The Gathering — Arena, and Gwent, Hearthstone is still at the top.

Hearthstone also one of the most popular games on the livestreaming site Twitch, and its viewership grew 14.5 percent in the year’s second quarter. On Twitch, fans like to watch players like Octavian “Kripparrian” Morosan play casually and competitively. Blizzard supports Hearthstone’s esports scene with a steady supply of sponsored tournaments.

Valve is launching its digital card game, Artifact, in November. It could bring new competition to Hearthstone and help expand the digital card game market further. Hearthstone next expansion, The Boomsday Project, launches on August 7.