Ruth Deech, the principal of St Anne's College, said yesterday that the university may have to examine what it is rewarding when it awards a first-class degree.
As Dr Margaret Spear, an educational researcher, arrived at the university this month to begin a 10-month investigation into women's relative under-achievement, the reasons were being fiercely debated.
Mrs Deech, who came to Oxford as a student 30 years ago and stayed, said the women's methodical approach to finals might be militating against them.
"It appears women are much more conscientious, very careful to get their facts right and present the arguments beautifully. Men will have a brave go at a brand new theory. It may be a question of style. Which should we be rewarding?"
Although women gain fewer firsts than men - 14 per cent compared with 23 per cent - a higher proportion gain 2:1s and fewer female students get thirds.
Standards have improved in the past 20 years, but the increase in women getting firsts has been smaller than the dramatic improvement in men's results.
At most other universities, apart from Cambridge where female students have a similar experience to their counterparts at Oxford, women's performance is similar to men's although they still achieve fewer firsts.
Dr Margaret Spear is to examine possible causes including Oxford's one-to-one tutorial teaching and the highly pressurised examinations which assess the degree in intensive three-hour papers at the end of the final year.
Mrs Deech said she thought the stress of finals might contribute. Her experience was that the cleverest women undergraduates reacted badly to the pressure created by the expectation of success.
And Derek Wood QC, principal of the former women's college St Hugh's, pointed out women 20 years ago had to be brilliant because there were only five women's colleges compared with five times that number reserved for the opposite sex.
He saw "nothing to choose" between men and women as they went through their courses. "You can't see the women struggling against the men. But it does seem that a higher proportion of women don't do themselves justice in finals."
Both heads dismissed claims that the disappearance of the single sex colleges was to blame. Most went mixed partly because they were failing to attract the best students.
Undergraduates outside the English faculty yesterday had their own theories.
"The teaching staff is very male, Oxford is a male domain. Two of my tutors are blatantly misogynist," said one 23-year-old finalist.
A first-year, aged 19, said most tutors tried not to be sexist but were "vaguely unenlightened" without realising it. "And one thing you do twig very quickly is women are in the minority."
About 44 per cent of undergraduates are female but fewer than seven per cent of the professors are. As a first is now almost obligatory to win post-graduate funding, Oxford women's failure to win them reduces their chances of becoming academics.
Joanna Innes, who chairs the university's equal opportunities committee, said they needed to narrow down the current ideas about what was wrong.
And Dr Spear, who has previously investigated gender differences in schools, said she hoped to be practical. "I think it is most productive to concentrate on factors where there is a possibility of bringing about change."
Sally Copley, vice president (women) of the students' union, welcomed the investigation - "although appointing a researcher and acting on the results are quite different things."
But there were also words of reassurance for women. Mrs Deech said she believed they often gained more from their time at Oxford than men. "Far too many men spend their university careers having a beer and playing football while women do drama and teach orphans in Romania," she said.
"I always say you should look at people when they are 25 or 30. There is more to life than just getting a first."Reuse content