As covered by Axios, in a report from IAM/PwC. As noted in the notes below the chart, these figures are based on a sub-set of the market, 20 advertising outfits. No doubt, they represent a huge part of revenue however. It’s hard to imagine that there’s many more millions in podcast advertising.
Also as highlighted by Sara Fischer:
Edison Research and Triton Digital estimates 98 million U.S. adults listen to podcasts.