Study author Laura Lindberg of the Guttmacher Institute in New York analyzed data on 15- to 19-year-olds teens from the 2002 National Survey of Family Growth.

"Our research shows that this supposed substitution of oral sex for vaginal sex is largely a myth," Lindberg says in a statement. "There is no good evidence that teens who have not had intercourse engage in oral sex with a series of partners."

The study, scheduled to be published in the July issue of the Journal of Adolescent Health, found 55 percent of 15- to 19-year-olds have engaged in heterosexual oral sex, 50 percent have engaged in vaginal sex and 11 percent have had anal sex.

Both oral and anal sex are much more common among teens who have already had vaginal intercourse than among those who haven't, suggesting that teens initiate a range of sexual activities around the same time, rather than substitute one for another, Lindberg says.

While only 1-in-4 teen virgins reportedly engaged in oral sex, once teens have had vaginal intercourse, the proportion increases incrementally, Lindberg says.