The survey by the Australian Research Centre for Sex, Health and Society, at La Trobe University, has highlighted the vulnerability of teenagers, especially girls.
The fourth National Survey of Secondary Students and Sexual Health, involving 2926 students from 105 schools in state and private schools, was done last year in all states and territories.
The survey of the sexual experiences of the students, in years 10 and 12 found that the most common reasons for unwanted sex were pressure from a partner or just being drunk.
Researcher Anthony Smith said that, strikingly, girls in year 12 were having more sexual partners and drinking 30 per cent more than they did when a similar survey was done in 2002.
Smith said that the extent of unwanted sex detected in teenagers underscored the need for sex education in schools to better explain links between underage drinking and sexual behaviour that might be accompanied with regret later.
The survey has indicated a healthy awareness of safe-sex messages in teenagers.
Condom and contraceptive use was generally high among those who were sexually active.
Overall, one fourth of year 10 students, and more than half of year 12 students, said they had had intercourse.
Professor Smith said that the average age of the year 10 students was 15 and the year 12s was usually 17.
About a third of year 10s and almost 60 per cent of year 12s reported having had oral sex.
Smith said that it was notable how diverse sexual habits and behaviour were among contemporary youth.
''We are not seeing broad general trends but changes that are gender and year-level specific,'' he said.
While adolescent girls were becoming more sexually active generally, rates for boys had remained stable or had fallen slightly since 2002.
Today's teenagers were more sexually active than any other generation, and they appeared not to be embarrassed about asking for information about sex.
A high number - 88 per cent - had actively solicited information from adults and peers. The main source for girls and boys was their mother (56 per cent), female friends (55 per cent) and school education programs (49 per cent).
And 90 per cent of teenagers who were sexually active indicated they wanted to have sex.