Clear Channel Communications Inc. is selling radio ads that are shorter than this sentence.

Commercials lasting only five seconds -- and some two-second ads called "blinks" -- are in demand by marketers. Clear Channel stations are also offering blinks that are just one-second long, but they haven't found any takers -- yet.

Clear Channel started offering the super-short spots in hopes of bringing in more ad dollars, part of a broader effort to revive ad sales in an industry hurt by competition from other media and listener fatigue with commercial overload. CBS Corp.'s CBS Radio, the No. 2 radio company after Clear Channel, has sold five-second ads as well, including some this year for TV networks.

Unlike traditional radio ads, which tend to run 60 seconds in minutes-long commercial breaks, the minimessages can be tucked in between individual songs in a series. Marketers hope that positioning gives them a better chance of being heard, since listeners often change channels when a commercial break starts. Of course, the brevity of the spots also makes them easier to miss.

Clear Channel is pricing the five-second spots, called "adlets," at 18 percent to 21 percent of a standard 60-second ad, which in a top-10 station in a major market can go for about $800, media buyers say. Two-second ads cost even less -- 10 percent of a 60-second ad, or roughly $80.

So far, Clear Channel has sold adlets to about 12 national advertisers, along with a slew of local marketers. Among them is General Electric Co.'s NBC, which recently bought five-second spots to hype its new drama "Heroes," about humans with superpowers. "I think I can fly," says a man. A voice-over immediately chimes in, "Heroes on NBC.

"We think adlets will be noticed more and stand out more," adds Tim Farish, vice president of media planning at NBC's in-house ad agency. The network is pairing the five-second spots with 60- and 15-second ads. "We wanted to use blinks but realized it was too difficult to squeeze the message into that length," he says. Some other advertisers, relying solely on adlets to get their message out, are sprinkling the short spots through the course of a day.

Not all ad executives are enthusiastic. "It's the dumbest thing I have ever heard," says Matt Feinberg, the senior vice president for radio at Zenith Media, a media-buying firm owned by Publicis Groupe, who thinks it is very difficult to get a message across in just a second.

"With the one-second-ad, there is a lot you can't communicate. You really need one and a half to two seconds to get that point across," concedes Bob McCurdy, regional president of sales for Clear Channel Radio, which has nevertheless not abandoned the idea of one-second blinks.

So far, only News Corp.'s Fox has bought any two-second spots, which it used to promote the season premiere of "Prison Break," "House" and "The Simpsons." The Simpson ad said: "D'oh!" quickly followed by "Tonight on Fox."

"We are thrilled with them, and we will continue to do more of them," says a spokesman for Fox.

To ensure the short ads don't further clutter the ad-heavy radio airwaves, Clear Channel says it limited how often it will run the new spots. Only one adlet and two two-second blinks will run per hour on any given station, says Mr. McCurdy.

Radio is "agnostic" about the length of spots it will run, according to Les Hollander, senior vice president and regional manager. "Instead of pushing a specific length, we try to listen and find out what commercial length fits their (marketers') objectives."

Seconds-long ads have turned up on TV as well: General Motors Corp.'s Cadillac and Time Warner Inc.'s AOL have used five-second ads. The TV world largely uses 60-, 30- and 15-second ads. Today, 30 seconds is the most common length for TV spots, but over the past 18 months, advertisers seeking to get their messages out have been embracing other lengths as a way to stand out.

Cadillac's five-second spots that debuted in 2005 were seen as a success on Madison Avenue and have even won industry awards.

In 1974, Master Lock, the padlock maker, made headlines when it aired a one-second TV ad during the Super Bowl, which featured a bullet flying through a Master Lock padlock.

Clear Channel's seconds-long ad pitch is the latest phase of a broader effort by the company to sweeten the appeal of advertising on its 1,100 stations. In 2004, in an initiative it called "Less is More," the broadcaster began to cut back the number of commercials it runs by 15 percent to 20 percent, a response to critics who complained that commercial overload was driving away listeners. In the second phase of the initiative, which began in 2005, it started encouraging marketers to buy 15- and 30-second ads, common in television but less usual in radio.

These moves came after several years of stagnant industry revenue, which had coincided with radio stations running an increased number of commercials. In 2004, radio stations averaged 14.9 minutes of ads an hour, while some stations were running as many as 22 minutes, according to Wall Street firm J.P. Morgan Chase.

JP Morgan analyst John Blackledge says the heavy ad load is contributing to the erosion of listenership. Indeed, a survey of 401 radio listeners conducted last year found that 13 percent switched the station as soon as a program went to a commercial, while another 20 percent switched after hearing one ad. More troubling for advertisers, the study, by Denver research firm Paragon Media Strategies, showed younger listeners were significantly more likely to switch the channel.

Young people are likely switching away from ads in increasing numbers because there are far more choices for them to find commercial-free music today -- from satellite radio to iPods.

Because of the Clear Channel cutbacks, other radio stations have begun to cut back on ad load, says J.P. Morgan's Mr. Blackledge. As a result, the average amount of ad time on radio stations in the U.S. has dropped to 10.8 minutes per hour, he says. Still, he adds, some stations are running up to 17 minutes of ads per hour.

Clear Channel boosted its radio-ad revenue 5 percent in the first half of this year, after suffering a dip last year after it cut back its ad load. The increase contrasted with a 1 percent decline in radio-industry ad revenue in the first seven months of the year.

Still, ad executives say radio has to do more. The radio industry "needs something that says commercials in radio are not an opportunity to change the channel," said Kevin Gallagher, a media director at Starcom USA, a unit of Publicis Groupe.