Psychologists have identified 237 reasons why men and women have sex.

While love and attraction remain the clincher for many, for others it is about getting closer to God; gaining a promotion; revenge; or a way to get rid of a tension headache.

Some of those asked said it was a reasonably effective way of overcoming boredom or burning up calories, while a few were attracted by the idea that it kept them warm, helped them fall asleep, or eased the stress of the day.

The results of the biggest study of people's motivation for sex show that men are more likely to spring into action for physical reasons than women, whose motives were more likely to be based on emotions. Women were much more likely to say: ''I realised that I was in love." Men were more likely to say: "I wanted to increase the number of partners I had experienced."

"We identified 237 distinct reasons why people have sex," the researchers said. "The study provides perhaps the most comprehensive exploration to date of the reasons people give for having sexual intercourse. They ranged from the mundane ??'It feels good' ??to the spiritual ??'I wanted to feel closer to God'. They ranged from altruistic ??'I wanted the person to feel good' to manipulative ??'I wanted to get a promotion'."

For the two-part study, reported in the Archives of Sexual Behavior this week, psychologists at the University of Texas quizzed more than 2,000 men and women aged 17 to 52.

"Why people have sex is a surprisingly little studied topic. One reason for its relative neglect is that scientists might simply assume that the answers are obvious," say the researchers.

While being attracted to the other person was the main reason for both men and women, the results show that for some the reasons were not so mainstream. Each of the 237 reasons was given the highest rating by at least one of the people taking part.

"The frequently endorsed reasons for having sex, reflect what motivates most people most of the time: attraction, pleasure, affection, love, romance, emotional closeness, arousal, the desire to please, adventure, excitement and opportunity," say the psychologists.

"The less frequently endorsed reasons, however, may be no less important. One person's seemingly trivial reason for having sex might well be another's magnificent obsession."