University of Texas at Austin psychology researchers David Buss and Cindy Meston uncovered 237 motivations for having sex that range from the mundane, "I was bored," to the spiritual, "I wanted to feel closer to God," from the altruistic, "I wanted the person to feel good about himself/herself," to the manipulative, "I wanted to get a promotion."

The study, published in the August issue of Archives of Sexual Behavior, identified four major factors for having sex:

-- Physical reasons such as to reduce stress, feel pleasure, improve or expand experiences and the physical desirability of their partner.

-- Goal-based reasons, including utilitarian or practical considerations such as "I wanted to have a baby," "I wanted to be popular," or "I wanted to give someone else a sexually transmitted disease."

-- Emotional reasons such as love, commitment and expression -- "I wanted to say 'thank you.'"

-- Insecurity-based reasons, including self-esteem, a feeling of duty or pressure or to guard a partner from straying.