Tru Spot! Online Radio:

In the United States, commercial radio stations make most of their revenue by selling airtime to be used for running radio advertisements. These advertisements are the result of a business or a service providing a valuable consideration, usually money, in exchange for the station airing their commercial or mentioning them on air. The most common advertisements are “spot commercials”, which normally last for no more than one minute, and longer programs, commonly running up to one hour, known as “informercials”.

The United States Federal Communications Commission (FCC), established under the Communications Act of 1934, regulates commercial broadcasting, and the laws regarding radio advertisements remain relatively unchanged from the Radio Act of 1927. In 2015, radio accounted for 7.8% of total U.S. media expenditures.