A survey examining sexual practices of US teens has undercut the notion that many engage in oral sex rather than intercourse to stay "technically" virgins.

The findings, published in the Journal of Adolescent Health, were based on answers by 2,271 females and males age 15 to 19 in 2002 in response to a government survey.

The researchers found about 55% of the teens said they had engaged in oral sex but that this practice was far more common among those who also had engaged in vaginal sex.

Teens said they began vaginal and oral sex at roughly the same time - by six months after first vaginal intercourse, 82% had also engaged in oral sex, according to the study.

"There is a widespread belief that teens engage in nonvaginal forms of sex, especially oral sex, as a way to be sexually active while still claiming that, technically, they are virgins," Laura Lindberg of the Guttmacher Institute in New York, who led the study, said in a statement.

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

The Guttmacher Institute studies sexual and reproductive health issues. About one in 10 of the teens said they had engaged in anal sex. These teens were far more likely to have also engaged in vaginal sex. "Teens of white ethnicity and higher socioeconomic status were more likely than their peers to have ever had oral or anal sex," the researchers wrote.