Meet the Men Having Sex With Strangers to Help Them Have Babies Donors offer their sperm for free in a method called "natural insemination."

 -- Once upon a time, when single women and infertile couples wanted a baby, they would pay a sperm bank to help them. Sometimes it costs thousands of dollars for a successful pregnancy. But now, those services have gone online, and at the click of a mouse, donors make their sperm available by offering to have sex for free. It's a surprising -- and some say unconventional -- method of making a baby called "natural insemination."

Donors connect with women on the Internet who want to become mothers "the natural way," because the recipients believe having sex maximizes their potential for getting pregnant.

ABC News' "20/20" talked to one sperm donor who calls himself "Joe" and says he's fathered more than 30 children.

“I’m not having intercourse with these women when there’s no chance of pregnancy,” he said.

Joe, a married man with three teenage children, asked "20/20" to hide his identity because of the double life he said he leads online as a "natural" sperm donor. He said his wife doesn't know about his extracurricular activities, but he has written a book about his experiences entitled, “Get Pregnant for Free on the Internet with a Private Sperm Donor.”

“I have a Clark Kent life. Then, I have the Superman life,” Joe said. “People might want to have millions of dollars in the bank, and then, you know, some of us might want to have dozens of children out there.”

When he is not working as an Internet entrepreneur, Joe travels around the country to impregnate women from every walk of life. Sometimes Joe ships his sperm for artificial insemination, but he often donates by having sex.

After seven years, Joe said he has slept with over 100 women for natural insemination.

“I'm unable to have as many children as I want in my relationship, and that would be unreasonable to ask a woman to give birth to 30 children,” said Joe.

When asked how many children he expected to have over his lifetime, Joe's answer was surprising.

“The World Health Organization said I can get up to 2,500, but I don't think that will happen in my lifetime. The other donors I know who have a lot [of children] are up there around the 100 range. I'm standing on the shoulders of giants.”

“I have the satisfaction of knowing that I have another descendant out there,” Joe said. “It’s not the road. It’s how we get there, if we actually get there.”

Kyle Gordy is also a donor. In addition to pursuing his master’s degree in accounting, he offers his sperm for free to women who want a baby.

“I don’t do any drugs. I don’t smoke. I don’t drink. I don’t drink caffeine. I eat only sperm-friendly food: wheat, brown rice ... fruit and vegetables,” Gordy told “20/20.”

The 23-year-old said he has what it takes to be anyone’s father. “Right now I’m attending university. Both siblings are engineers. The nuclear engineer is my twin. My grandpa was a scientist,” said Gordy.

On his online advertisement to be a sperm donor, Gordy posted photos of himself as a child and as an adult and information about himself, including his hair color and IQ.

No question is off limits for prospective sperm recipients who contact Gordy, who's been asked: “‘Is your sperm good? Have you had success in the past? How do I know you’re going to get me pregnant? How do I know you won’t flake?’”

While he doesn't get paid for donating his sperm, Gordy said his purpose is not about sex, but about creating new life.

"I’m passing on my legacy and giving these people kids,” Gordy said.

In fact, Gordy said his first child was born recently. “I feel like, wow, I did it,” said Gordy.

One of Gordy's sperm recipients, 44-year-old Serena, asked “20/20” to conceal her identity. She recently drove two hours to be naturally inseminated by Gordy at his home. Serena said she’s never been married and longs for a child.

“Always, since I was a very young child, and sometimes career and life just gets in the way,” the insurance broker told “20/20.” “Then oops, I’m 38. Oops, I’m 40.”

Though she’s thought about going the traditional route and getting married, Serena said dating is difficult.

“I don’t care if I have a husband or a man, I just want the child,” said Serena.

Serena was also unable to afford the fees at a sperm clinic. Sperm banks such as California Cryobank have strict standards screening for disease, genetic history and even physical characteristics. A vial of sperm costs about $700.

After turning to the Internet for help, Serena said the words “free sperm” led her to Gordy.

“[I felt] that there’s maybe no other alternative for me. My clock is obviously ticking loud and louder every day,” she said.

Serena will also soon find out if she’s a mother at last. She said she’s prepared for what she will say to her child about his or her father.

“Kyle and I like to think of ourselves as friends too,” Serena said. “My friend is my donor.”

Serena is just one of many other women online eager to become pregnant. Another natural insemination recipient already has a 4-year-old son, but wanted another child. After she split from her boyfriend, she began searching for options.

“I think just always growing up thinking I’d find the right man and always had that fairy tale growing up,” the woman told “20/20.” “Hopefully, I find the right man, eventually, but maybe he won’t be the biological father of my children.”

Three tries with artificial insemination where she inserted donor sperm herself failed, so she tried natural insemination.

“I had read a couple of books that talked about fresh semen being a lot more effective than frozen sperm,” the woman said.

She said she found hundreds of men online to choose from, but she chose a man who advertised his “intelligence.” The two met at a local coffee shop.

“I thought he was cute,” the woman said. “But, yet, I had to keep reminding myself, ‘This is a donor, not a date.’”

They had sex only once, but she is still deeply affected by the memory as she waits to find out whether she is pregnant.

“I felt it was sad, at least for me, but it’s the route I’ve chosen,” the woman said. “And I want my son to have a sibling, most of all.”