By day, Ed Houben is a mild-mannered, 44-year-old bachelor who works as a tour guide in the Dutch town of Maastricht, where he lives.

On nights and weekends, however, Houben comes alive as his alter ego: Europe’s most prolific sperm donor, and one who prefers to contribute the old-fashioned way.

“Sperm cells are like candy at Mardi Gras,” Houben says. “The more you throw out, the better you get.”

Houben says he has 99 known children scattered around the globe. “I have children in Australia, Israel, Canada, Austria, Germany, Belgium, France, Luxembourg, Italy, England,” he says. “There are also the possibles” — the women he had sex with whom he never heard from again.

“At the beginning, I would assume they were angry with me,” he says. “Then later, several people came back and said, ‘We were afraid you’d want to get involved in our lives. But now we want another one.’ ”

If there’s one thing that remains constant about Ed Houben, it’s that he’s always ready to give. And he says his methodology is the kindest there is.

“A normal person would prefer to feel desired by a man who wants to have children with her,” he says. “No woman grows up hoping to meet a knight in shining armor with a syringe.”

Houben grew up in a lower-middle-class family, the youngest of six children. He was an accident. “My mother said, ‘Oh, I forgot to take the Pill for two days, and then we had you,’ ” he recalls. “But these things don’t traumatize me. If anything had gone different, there would be 99 less children in the world.”

He first considered donating sperm when he was 18, and an older couple he knew was ­lamenting their childlessness.

“Sperm cells are like candy at Mardi Gras,” Houben says. “The more you throw out, the better you get.” - Ed Houben

“They said they’d been trying to conceive for 10 years,” Houben says, “and it astonished me. I thought good people would always have children. I thought it might be something I could help with, but I was too bashful to offer anything back then.”

Eleven years later, he took the plunge, calling the sperm bank at the Academic Hospital in Maastricht. There, Houben says, he was under the care of Dr. Gerard Dunselman. (The doctor did not comment for this story, but still works in the hospital’s department of obstetrics and gynecology.) From 1999 to 2005, Houben says, he donated 25 times, all anonymously.

“They specifically asked me not to tell, and I began to hate that more and more,” Houben says. When he hit his maximum at the hospital, he began going to other clinics in the Netherlands. He did not worry about the potential ramifications.

“The doctor and I were becoming pretty good friends, and I said, ‘Do I need to stop? Is there some kind of genetic danger here?’ ” Houben says the doctor assured him that with a population of 15 million, he could safely father 500 children in the Netherlands alone.

In 2002, he became an independent contractor of sorts. Houben started a Web site, posted all his STD test results, and began accepting requests from women all over the world.

He doesn’t claim to have an unusually high IQ or great athletic ability, and as his photos make clear, he’s not a chiseled paragon of youth and beauty. But he advertises himself as having exceptionally potent sperm, and if you’re a woman desperate to get pregnant, he will give it to you, for free, as many times as it takes.

“Only one-third of men have strong enough sperm to be frozen and defrosted, and only one-third of them are capable of fertilizing eggs after thawing,” Houben says. “So I’m one-third of one-third.”

Not true, says Dr. Joseph Alukal, director of male reproductive health at the New York University School of Medicine. “Sperm preservation is very commonly done,” he says. “It’s very rare that sperm does not survive freezing. This might be part of his marketing.”

“It’s not awkward to have sex with someone you’ve met two hours before. Have you seen American sitcoms?” - Ed Houben

Still, like Michigan’s Kirk Maxey, who fathered 400 children, and an unnamed Virginia man who spawned more than 129, all through sperm banks, Houben is free to keep plugging away. There are still no governmental regulations, in the United States or Europe, placing limits on sperm donation.

Following a recent BBC interview, Houben says he has received 72 requests in the past month — but he won’t accept just any woman.

“With most of them, it starts with the e-mail,” Houben says. “If she’s not dyslexic but she makes mistakes every second word, it’s not my cup of coffee.”

If a woman clears that hurdle, next comes the clinical exchange. “Of course, I ask medical histories — HIV, syphilis, chlamydia . . .” Then comes perhaps the most delicate question of all: What do you look like?

He says that he has never fallen for one of his clients but that attraction is important.

“I’m not a machine,” Houben says. “I can’t force myself to find someone attractive. So a healthy lifestyle is important. Like, I got a request from Texas last year. Something gave me the feeling that I needed to ask, ‘What is your height and weight?’ I think she was 5-foot and 300 pounds. I said, ‘You know, I’ll be happy to talk to you when you go on a diet.’ ”

Houben says having sex with him is not required, but he insists it’s the most advisable. “On average with me, artificial insemination takes one to 12 months, but the natural way takes one to three cycles.” In the beginning, he says, it was the women who would ask to sleep with him.

“Of the 12 women who had a doctor title — and, OK, one was a doctor of philosophy — almost all chose the natural method,” he says. “They’re working all day with syringes and petri dishes — that’s the job. And this is their personal life.”

Houben charges no money for his services, partly because it’s ­illegal to buy and sell human ­material in the Netherlands and partly because he sees himself as a true humanitarian.

“I could have joined the Peace Corps,” he says. “But I stumbled into this.”

Nearly all of his clients travel to him, and Houben puts them up in his modest flat. He went so far as to redecorate his master bedroom at a cost of nearly $14,000 a few years ago. He never uses alcohol or any other mind-altering substances. He says he spent much of his life shy around the opposite sex and has learned what he knows about women through these transactional assignations.

For example:

“Stupid people have better sex, because they don’t think about things so much. They just enjoy.”

“It’s not awkward to have sex with someone you’ve met two hours before. Have you seen American sitcoms?”

“For me, basically a shy guy with women, I’ve become more assertive. In a short time, I have to make the assessment: What does this woman prefer? I always invite them to tell me what they want.”

If a woman arrives alone — which she rarely does — Houben will have sex with her in the master bedroom. “I try to be the perfect gentleman in every way and not look like the ex-murderer who just got sprung,” he says.

Far more common are couples, and logistics can be complicated. While Houben and the woman retire to another room, the men will sometimes “stay in the living room and watch TV, read a book,” he says. “It’s important they be there to support the women in the creation of life.”

Houben will then let the couple stay the night in the master while he takes the smaller guest room.

Other times, the men prefer to be more involved. Some will sit in the room and watch. For others, that’s not enough.

One client, an artist, introduced Houben to her boyfriend on their third attempt. He asked if he could be in the room, and Houben said yes.

“She was very happy,” Houben says. “So I said, ‘Steve’ — let’s call him Steve — ‘I’ll take it from here.’ But he already had his pants down! I thought, ‘I hope I don’t feel a hairy hand between my buttocks! But after two hours of combat, I thought, ‘He doesn’t want anything from me. He just wants to be present at the creation of his child.’ I could handle it.”

The only thing that still troubles Houben is a woman who would rather not have sex with him. “I do feel rejected as a person if someone wants artificial insemination,” he says. “Yesterday, I responded to someone in Brazil who wanted artificial ­insemination.”

Houben administers this by ­going to the pharmacy and buying a plastic cup and syringe, then “doing the voodoo that I do so well” in the bathroom. He gives his sperm to the woman and leaves.

With the woman in Brazil — as with all women who request artificial insemination — Houben makes it clear that any other client who prefers the natural method will always come first. And he is a very busy man.

“You know, no ovulation tests bother to ask me if I’ve worked a 14-, 16-hour day,” he says. “I’m still a person. I have to eat, sleep, clean my house . . . It’s stress.”

And even a man as fertile as Houben is not immune to performance anxiety. “I actually try to keep the image in my mind,” he says, “that men are always ready for action.”

Houben’s last relationship was long-distance and lasted two years. He says what ultimately broke it apart was not his sleeping with other women — it was that he couldn’t get his girlfriend pregnant.

“I’m not lying awake here that I don’t have a family,” he says. “But my plan is to find the woman of my life, and if she wants me to stop, I’ll stop. And if she wants to have children, I would do that.”

Houben has no legal documents drawn up. He feels protected enough by Dutch law and the quality of people he has chosen to help. He visits with some of his children and always leaves how much contact — if any — up to the parents. He does not think there will be any fallout from his continuing work. In fact, he says he’s doing would-be mothers around the world a service.

“I get e-mails from Turkish men, Indonesian men saying that if I have too many women, they’d like to help,” Houben says. “If I stop, I have to leave the women to these guys.”

It’s quite the quandary: “I cannot help everybody,” he says. “I cannot solve all the problems in the world.”

NYU’s Alukal, for one, wishes Houben would stop ­trying.

“If someone reading this were to think, ‘I’m going to fly to the Netherlands and meet this man and have sex with him to have a baby,’ I would say, clear as day, ‘This is not a bright idea.’ ”