U.S. TV networks are adding hours to their coverage of this week’s GOP National Convention, and there’s a simple reason: demand from advertisers.

Reuters reports that coverage is up from four years ago. “The stakes are high for broadcast and cable networks,” the report notes. “Media analysts predict viewership for Trump’s acceptance speech could surpass the record 38 million who watched Barack Obama address the Democratic convention in 2008.”

TV advertisers spent $5.8 million during the two conventions in 2012, down from $7.8 million in 2008, according to Kantar Media, the report notes.

“The potential for the unexpected at what is usually a meticulously staged event is driving strong advertiser demand, network executives said. CNN is pulling in between $40,000 and $100,000 for 30-second spots, a source familiar with the matter said. That is far above the typical cost of roughly $7,000 for a primetime ad on CNN,” Reuters reports.