Radio advertisements are broadcast as radio waves to the air from a transmitter to an antenna and a thus to a receiving device. Airtime is purchased from a station or network in exchange for airing the commercials.
While radio has the limitation of being restricted to sound, proponents of radio advertising often cite this as an advantage.
Radio is an expanding medium that can be found on air, and also online. According to Arbitron, radio has approximately 241.6 million weekly listeners, or more than 93 percent of the U.S. population