The hottest destination for television advertising these days isn’t traditional national TV. Rather, streaming platforms are gobbling up a growing share of ad dollars as their audiences expand.

After increasing rapidly in recent years, streaming ad spending is projected to approach $20 billion by 2029, not far off linear TV ad spending, according to estimates from ad consulting firm Madison and Wall.

The shift is expected to be a major theme at this week’s celebrity-studded upfront ad-selling event, when media and tech giants will be making a full-court press to convince brands to commit billions to their TV networks and streaming platforms.

While the launch of ad-free streaming services like Netflix initially provided relief to consumers who had grown weary of long TV commercial breaks, the ad-supported streaming model has proven more popular of late.

Ad-supported plans now represent almost 50% of all premium subscription video-on-demand sign-ups in the U.S., up from 39% just two years ago, according to research firm Antenna.