Who’s Cheating? Approximately 40% of men seek sexual satisfaction outside their relationships, says Kat Hertlein, Ph.D., professor of human development at the University of Nevada, Las Vegas, and a marriage and family therapist.That number hasn’t changed much since 1950, when the famous Kinsey sex study found that 50% of U.S. men cheat at some point in their marriages.Why They CheatThe No.1 reason: Men crave sexual variety, according to David Buss, Ph.D., professor of psychology at the University of Texas and author of the foreword of The Consuming Instinct (Prometheus Books).

He’s unhappy with his mate – and extramarital sex is cheaper and easier to get these days, Dr. Buss says.He has plenty of chances. “Power wives” beware: Being married to a high-profile guy ups the odds he’ll wander.