Some couples keep a strong sex life going for decades.

One of the largest studies to-date on sexual satisfaction in long-term relationships, to be published in the Journal of Sex Research later this month, has found that couples with satisfying sex lives do a lot of communicating. Researchers also cited the importance of working to set the mood, practicing sexual variety and oral sex, and frequently having orgasms and sex.

The study also found that the men and women who said they were sexually satisfied were happier in their relationship.

To conduct the study, researchers at Chapman University, in Orange, Calif., California State University, Los Angeles, Sonoma State University in Rohnert Park, Calif., and at the Kinsey Institute at Indiana University in Bloomington, Ind., which studies human sexuality, posted a survey on MSNBC.com for two weeks in 2006. They then analyzed the answers of almost 39,000 married or cohabitating heterosexual men and women who had been with their partner for at least three years. The average age of the sample was 40 years old for women and 46 years old for men.

Individuals were asked to rate their current sexual satisfaction on a scale of one to seven, and also to rate their sexual satisfaction in the first six months of their relationship. An overwhelming majority—83 percent—of respondents recalled being satisfied in the first six months. But only about half—43 percent of men and 55 percent of women—said they were currently satisfied. The rest said they were feeling “neutral” (16 percent of men and 18 percent of women) or dissatisfied (41 percent men and 27 percent of women).

Researchers are comfortable using anonymous surveys when the data sample is large and broad. The work is just being published now because it typically takes several years for researchers to analyze such a large quantity of data and for their work to go through a vetting process by peers and editors.

For starters, people who are satisfied with their sex life are having sex with their partner much more often than those who are dissatisfied, the study found. Seventy-nine percent of men and 81 percent of women who were satisfied said they have sex one or more times per week. Only 17 percent of dissatisfied men and 23 percent of dissatisfied women said they have sex that often.

Click for more from The Wall Street Journal.