SAN JOSE, Calif. — Sitting in his brightly lit, third-story corner office on a leafy street in Palo Alto, Andrew Conru looks like a typical Silicon Valley entrepreneur. He wears spectacles and a blue button-down shirt. The racing bike he rides to work is propped in his office.

The sandy-haired 38-year-old Stanford Ph.D. speaks in a measured manner about the companies he has started over the last 13 years, one of which reportedly generates hundreds of millions of dollars a year in revenues and is highly profitable.

So why aren't venture capitalists rushing to throw money at him? Because Conru runs one of the best-known but least discussed Web destinations, Adultfriendfinder .com, "the world's largest sex and swingers community."

Bawdy, yes, but also lucrative. Consider that Adultfriendfinder — tops in revenue among the 40 sites run by Conru under the holding company Various Inc. — claims 25 million active users and an undisclosed percentage of them pay up to $50 a month for its services. The Web-measurement service Alexa ranks the site as the 58th-most popular on the Web.

In comparison, the social networking site Facebook, reportedly for sale for $1 billion, has around 9.5 million registered users who pay nothing. Its Alexa rating: 56.

But most investors can't do anything about Various other than watch it expand. Many firms have "sin clauses" with their financial backers that outline the types of companies they are strongly discouraged from backing, such as adult entertainment outfits.

An IPO is an option, but other competitors have attempted to go public and failed. And the stocks of publicly held adult-content companies get discounted heavily because so many investors, such as mutual-fund managers, can't buy the shares.

There also aren't many potential purchasers. Only a few adult-content companies are publicly held — including New Frontier, Private Media Group and Playboy Enterprises — and Conru says that his company is now worth more than they can afford.

Put another way, there's no easily "exiting" Various, in the parlance of the investment world.

"Although it's not illegal, adult content is akin to the drug trade in some ways," said James Hong, a friend of Conru and the co-founder of two startups, HotorNot.com, which rates users' looks, and SaveMyAss .com, a flower-ordering service. "It's hugely profitable but (getting out) can be difficult."

Parents were steelworkers

It's an unusual predicament for someone running one of the few dot-coms in Silicon Valley that is generating serious cash. Then again, Conru seems like an unusual person to run an adult Web site.

Born near Lake Michigan in northwestern Indiana, Conru grew up on a farm and started his first company at 8, selling vegetables door to door. He thanks his parents, who were steelworkers, for his work ethic, saying he learned by watching them "work the steel mills during the day, and farm at night."

He threw himself into work soon after arriving at Stanford in 1991, where he received undergraduate degrees in economics and engineering and a doctorate in mechanical engineering. In between classes, he founded his first company, FocalLink, a banner advertising network that was later acquired. He also created the early online dating site WebPersonals, as well as Dine.com, a restaurant-recommendation service.

Then came Friendfinder.com, launched in 1996. "It was going to be a friend-networking site where people could find a golfing buddy or romantic interest, but people began to post risque photos. When that didn't stop, I decided to launch Adult friendfinder.com."

And a few other Web properties. Among the 25 dating sites now under the Various Inc. umbrella are Alt.com, Jewish FriendFinder.com, French FriendFinder.com, Lesbian Personals.com and Senior FriendFinder.com. Alt.com is an adult-themed site with 3.8 million registered users; the others are regular, lightly visited, dating sites.

Conru, who is unmarried, says he regularly uses Adultfriendfinder. "I understand what goes on in our users' worlds by partaking in the process."

Profits aren't known

Some go so far as to suggest that Conru is obsessed with the business, which now employs 300 people, including 100 programmers.

"People seem to think that the adult business is easy, low-hanging fruit," Hong said. "But Andrew has been able to create sustainable competitive advantages over his competitors. That's why he is so profitable."

Exactly how profitable is a mystery. No one doubts the company is profitable, and Conru says the company has been making money since 1996, mostly through Adultfriendfinder.com and Alt.com. As for his personal wealth, Conru, who owns 90 percent of Various, says only that he is worth "more than $100 million." (The other 10 percent of Various is owned by Lars Mapstead, whose start-up, Cams.com, was acquired by the company last year.)

Perhaps the bigger mystery is what comes next for Conru, who rarely talks with the press, dislikes venture capitalists — "I'm rude to them," he said — and yet seems stuck in his enviable rut, with few options for selling, even to buyout firms. (Conru says that he has met with several and that they, too, "shy away from adult stuff.")

Whatever comes next, one senses that Conru could use a respite from his unlikely empire. Looking out the window, he sighs. "I do wonder, do I need another dollar? I've been doing this a long time."

"I do wonder, do I need another dollar? I've been doing this a long time."

Andrew Conru,

entrepreneur