LAS VEGAS (Reuters) - Matt Virtue, who works as a consultant at a Washington law firm, says he spends more than $10,000 (5,050 pounds) a year to attend conventions, hotels and clubs where he and his girlfriend can have sex with other partners.

Two couples who met and swapped partners the night before at the annual convention of Lifestyles, the largest U.S. swingers organization, are pictured together at a Las Vegas Hotel, Las Vegas, Nevada, August 11, 2007. The event features seminars, contests, pool parties and late night orgies for a middle aged crowd of mostly married couples in hotel suites. Matt Virtue, 40, a consultant without hat, lives with Michelle (in red bikini), 38, a government worker, outside Washington D.C., Harry (bald), 42, a computer specialist, lives in LA and his girlfriend is rock and roll singer Vickie Lynn, 43 (wearing sunglasses and hat). Picture taken August 11, 2007. REUTERS/Adam Tanner

“Any other hobby that I was into at 40 years old is going to cost me $10,000,” he said from a hot tub he was sharing with his girlfriend and a couple with whom they had been intimate the night before. “Dude, I’m addicted to it, there is no doubt about it.”

Such enthusiasm has turned what were once private passions into a multimillion dollar business. Lifestyles Organization, the nation’s largest swinger services company, has annual sales of about $15 million.

Swingers also bring in millions of dollars to specialty clubs and hotels in the United States as well as Jamaica, Mexico, France and elsewhere.

“We’re talking about a lifestyle, but in reality we are also talking about a business,” Robert McGinley, 73, the president of Lifestyles Organization, said during its annual convention in Las Vegas, which attracts about 900 couples.

Lifestyles Organization caters to a middle-class demographic who want to meet like-minded couples and who typically want to hide their passions from what they call “vanillas” (conventional couples).

Efforts to meet such couples outside those circles often fail, giving tour, club and convention organizers steady business.

Terri, 48, attending the convention from Boise, Idaho -- who asked that her last name not be published -- said she and her husband of 21 years spend as much as $8,000 a year on several weeks of swinging vacations and club visits.

At this year’s event, Anaheim, California-based Lifestyles Organization contracted out an entire hotel near the Las Vegas Strip and organized seminars and parties for middle-aged couples.

The most exhibitionist of those gathered in open hotel rooms after midnight to have sex as others watched or joined in. Some couples made small talk as they were engaged in sex, including one man who boasted that his son was in medical school.

“The other night I looked up and there were five or six people looking,” said Terri, who retired from the U.S. Air Force two years ago. “I’m glad I was giving them a good show.”

“I’ve had three (lovers) in the past 24 hours.”

Leading sex researchers say they do not know the number of swingers in the United States, so it is difficult to pinpoint how much business the subculture represents overall.

Rick Conner, a swinger and author of an advice book for such couples, estimates there are 100,000 U.S. swingers, of whom 20,000 are particularly active. Other swingers have suggested the number is in the low millions.

PLEASE, NO SEX IN THE RESTAURANT

Despite the unusual focus of the convention, McGinley shares the bottom-line concerns of many businessmen.

“In business there is risk and you have to decide is it a reasonable risk or not,” he said. “Behind the scenes there is a lot of planning that goes into this and a lot of going over financials, financials of the past and what is the current situation.”

He said couples paid a registration fee of $690, out of which $200 covered costs, leaving an overall profit of more than $400,000. Couples pay additionally for hotel rooms and flight costs.

Lifestyles Organization faced a few unusual incidents. His staff had to halt one couple from engaging in a sex act inside the Tuscany Suites restaurant.

Conventions bring Lifestyles $4 million in annual sales; their travel business booking swinging guests into resorts such as Hedonism II in Jamaica or Desire in Mexico bring in another $10 million to $12 million a year, McGinley said.

“We relax our already liberal rules to accommodate the Lifestyles Organization and make the entire resort clothing-optional,” explained Richard Bourke, general manager of Hedonism II.

He said Lifestyles Organization books $2 million of rooms a year over six contracted weeks. Hedonism II staff are barred from intimate relations with the guests and some have been fired for violating the edict, Bourke said.

“You have resorts with big-name resort companies that are catering to it,” McGinley said. “They’re not into swinging at all, but they are into making money, and we’re the ones that provide the clients for them.”

Desire Resort and Spa in Los Cabos, Mexico opened in November with a focus on the swinging market. About half of the guests are active swingers, according to Jesus Prado Leal, a receptionist.

Several hundred clubs nationwide also cater to swingers. Jeff James, who works for Club Freedom Acres in San Bernardino County east of Los Angeles, said 225 to 260 couples visit on a typical Saturday night, paying $85 each, with a similar number on Fridays paying $65. “It’s doubled in daily attendance in the last three years,” he said.

Swinging also boosts ancillary services such as breast enhancements and erectile dysfunction drugs. “Viagra is definitely part of the adult scene,” said Deborah, a 52-year old aesthetician grandmother from Dallas, Texas, who asked that her last name not be used. “Instead of four stars before, it’s probably five stars now.”