Researchers at UT have studied reasons college students have sex. Newspaper article and the study. The latter admits that the data are skewed by the fact that they were interviewing college students, and of these, “Four percent of the women and 2% of men were married. Six percent of women and 5% of men were living with a sexual partner.” They suspect that basic biological issues (e.g., having sex to have a baby) might figure higher in studies of people who aren’t college students.
There were nine themes that appeared to characterize the most frequently endorsed reasons for having intercourse: (1) pure attraction to the other person in general; (2) experiencing physical pleasure; (3) expression of love; (4) having sex because of feeling desired by the other; (5) having sex to escalate the depth of the relationship; (6) curiosity or seeking new experiences; (7) marking a special occasion for celebration; (8) mere opportunity; and (9) sex just happening due to seemingly uncontrollable circumstances.
Interestingly, “20 of the top 25 reasons given for engaging in sexual intercourse were similar for men and women.”
Update: Comments by David Neff at CT.