For more details, see The podcast industry expected to create $1 billion in annual revenue by 2021 | The Verge
"U.S. advertisers spent $479.1 million advertising on podcasts in 2018, up 53% from about $313.9 million a year earlier, according to a new report from the industry group Interactive Advertising Bureau and accounting firm PricewaterhouseCoopers LLC.Marketers Turn Up Podcast Advertising | WSJ
Podcast advertising is expected to rise to $678.7 million this year, the report said.
Ad spending on podcasts has remained relatively small compared with more established media, hindered in part by a lack of metrics and targeting capabilities.
Marketers are projected to spend about $70.83 billion on TV advertising in the U.S. in 2019 and about $129.34 billion on digital advertising, according to research firm eMarketer."