(PhysOrg.com) -- While young women's educational and career opportunities have skyrocketed over the past two decades, their opportunities for stable, long-term relationships have declined, according to new research from sociologists at The University of Texas at Austin.

In their new book "Premarital Sex in America: How Young Americans Meet, Mate and Think About Marrying," (Oxford, 2011) researchers Mark Regnerus and Jeremy Uecker detail the sexual attitudes, behaviors and experiences of Americans between the ages of 18 and 23. The research goes beyond the clichés about salaciousness within the largely white Greek system to provide a nuanced view of the experiences of a much wider swath of young adults.

"Hooking up gets all the attention but most sex occurs in relationships," says Regnerus.

In an era when marriage is often far from the minds of young Americans, the book provides a fuller understanding of why that is, how the place of sex in romantic relationships has shifted and what that means for young adults. The outlook for relationship security, he claims, is more grim than ever.

"There have been many changes in romantic and sexual behavior over the past 30 years," says Regnerus. "One is that the 'price of sex' among unmarried Americans has dipped to an all-time low."

Regnerus and Uecker describe the "price of sex" as the cost — to men — of romance, status, stability and commitment that men exchange for access to sex in a relationship. They argue that despite women's successes, contemporary relationships are becoming more male-centered than ever, with men gaining access to sex earlier and more often, yet providing fewer and later commitments than a generation ago.

"It is, in part, one of the unintended consequences of women's educational and professional success," Regnerus says. "Women no longer need men. When that's the case, how relationships develop will change. And they have.

"Men's economic and educational successes have stalled, creating an environment in which fewer educated and financially-stable men are selecting mates from a larger pool of educated and financially-stable women," he says. "It's created an imbalance that tips relationship power in the direction of the men. Instead of men competing for women, today women feel like they must compete for men."

The authors used data from four national surveys and dozens of face-to-face interviews to compile this unprecedented study.

also generally display few emotional consequences in their sexual choices, while women have a harder time dealing with "no strings attached" sex, the authors write. "For them, the strings are often what makes sex satisfying," says Regnerus. Women, he notes, also "seem to be happier when they’re in a relationship than when they’re not."

The book also looks at differing sexual attitudes and practices among conservatives and liberals. Conservatives tend to marry earlier but also divorce earlier, while liberals often exhibit a longer period of sexual experimentation before marriage.

Regnerus is an associate professor of sociology and a research associate with the Population Research Center at The University of Texas at Austin. He is also the author of "Forbidden Fruit: and Religion in the Lives of American Teenagers" (Oxford, 2007). Uecker earned his Ph.D. in sociology at The University of Texas at Austin in 2010 and is a postdoctoral scholar with the Carolina Population Center at the University of North Carolina, Chapel Hill.