In a study of more than 200 college students, 25 percent of men and half of the women reported that they'd acted out an orgasm during sexual activity.
The reason to fake it was to end the sex without the awkwardness of hurting their partner's feelings, reports a science weekly.
The new study, conducted by psychologists at the University of Kansas, asked 180 college-age men and 101 college-age women questions about their sexual histories.
Each participant was asked whether they had ever pretended to have an orgasm. To catch those who might be ashamed to admit their deceit, the participants were also asked whether they'd "done something similar" to pretending to orgasm.
Almost 100 percent of those surveyed had experienced some sort of partnered sexual stimulation, whether manual or oral. Just under 70 percent of the women and 85 percent of the men reported penile-vaginal intercourse.
Intercourse turned out to be a major predictor of whether someone had faked it. About 10 percent of men and 19 percent of women who'd had sexual encounters but not intercourse had faked orgasms, compared with 28 percent of men and 67 percent of women who'd had penile-vaginal intercourse.
Pretenders tended to be more sexually experienced, and were more likely to have had an orgasm at some point, either through masturbation or intercourse.
Penile-vaginal intercourse was also the most likely type of sex to trigger orgasmic acting. Of those who specified the type of sex during which they faked an orgasm, 86 percent of men and 82 percent of women reported intercourse.
The reason may be that people expect orgasm during intercourse, the authors wrote. Several men in the study reported faking an orgasm because they had no other way to end a sexual encounter without awkwardness.
The research is published in the November issue of the Journal of Sex Research.