In a string of surveys between 1991 and 1996, nearly 17 percent of men said they had ever paid for or received payment for sex. That fell to 13.2 percent between 2006 and 2012. Last year, that number hit the lowest point since the question was first asked - 9.1 percent - though statisticians caution that the unusually small number could be a fluke.
The survey drew no distinction between buying and selling sex, but men are widely assumed to be customers far more often than they are sellers.
The numbers seem to be shifting with the generations: Older men are much more likely to say they have bought or sold sex at some point in their lives. Younger men, in turn, have been less likely to report doing so than men of the same ages a few decades ago.
The numbers come from the General Social Survey, a project of the independent research organization NORC at the University of Chicago meant to track changes in American society.
The survey, funded principally by the National Science Foundation, has questioned more than 57,000 Americans since 1972. Nearly 11,000 men have answered the question about paying or being paid for sex since it was first asked in 1991.
Experts say there are trends that could be turning more men away from prostitution, including new technology and looser sexual mores.
The Internet - through websites such as Adult FriendFinder and smartphone apps such as Blendr - has made it much easier to find other people who want to have sex without charge, said Michael Reece of the Indiana University School of Public Health.
Reece said young adults who grew up "in the shadow of HIV" also might be more uneasy about prostitution. He pointed to the fact that condom use is higher among people in their teens and 20s than it is among older adults.
The dropping survey numbers might also be tied to the fact that modern men are less likely to have served in the military. Men who served are more than twice as likely to have ever bought or sold sex, the surveys show.
Buying or selling sex has also fallen somewhat among military men and veterans; several researchers suggested men might have found it easier to pay for sex in Vietnam or Western Europe than in newer battlegrounds such as Iraq.
Other experts are skeptical that men are actually changing their habits. The dropping numbers defy widespread concern that the Internet has made it easier to link prostitutes and clients. A recent Arizona State University study based on responses to online ads estimated that about 1 out of 20 men in a scattering of cities were seeking to buy sex online.
"I have never read anything that suggests a decline in men buying sex," said Melissa Farley, executive director of Prostitution Research and Education, a nonprofit that aims to abolish prostitution. She was especially dubious because the survey did not distinguish between those who buy sex and those who sell it.
So who is still buying sex?
In interviews with more than 100 men who bought sex, Prostitution Research and Education found 26 percent of customers said they were fulfilling immediate sexual urges, but 19 percent sought "variety" and 12 percent were looking for convenience or lack of commitment. The rest gave other reasons.
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