Ten or fifteen years ago, online dating was too new to be socially acceptable. But now, many people search for a partner online.

Online dating is very different from traditional dating, in which people spend time with one another, slowly learning about each other. With online dating, people learn a lot about a potential partner before even meeting them.

We spoke with Mario, who had recently moved to the city of Baltimore, Maryland. His friends paid for him to use an online dating site. He thought he knew just what he was looking for.

MARIO: "A non-American, non-scientist, nothing related with Latin. And I ended up with the completely opposite."

"Opposites attract" is a popular saying. But online dating companies say the more similar two people are, the more likely they are to have a relationship that lasts a long time.

One of the largest online dating sites is eHarmony. It asks people who want to meet someone using the site to first answer more than four hundred questions. A secret mathematical algorithm then uses the answers to match people. An algorithm is a step-by-step process for solving a problem.

Gian Gonzaga is the director of research and development at eHarmony. He spoke to us on Skype:

GIAN GONZAGA: "We like to say that opposites attract and then they attack. And it`s not that you have to be similar on everything. It`s only those things that are most important to you."

Makon Fardis is a clinical psychologist who works with couples. He does not believe in using mathematical algorithms to match people because, he says, only seven percent of people tell the truth when describing themselves.

He says even if people don`t decide to lie or mislead, the way we see ourselves is different from who we really are. He says there are many examples of couples that seem like they would be compatible, but are not when they meet.

Remember Mario? A woman named Tamara was his online match. She had some worries about online dating, but also saw the good, as well.

TAMARA: "One is that you just meet a lot of people and, you know people you may not encounter regularly. And the other thing, it was  easier like, if you didn`t have a connection, it made it easier to say, you know I`m just not, this isn`t what I want and you move on."

At first, Mario worried that Tamara was too similar to him. But he suggested they meet for coffee.

MARIO: "But then she ordered another drink, another drink. And let`s order something to eat. And it was like `OK.`"

TAMARA: "It was very natural -- we were just blah, blah, blah the whole time. And it ended up being five hours later that we had dinner and everything."

That was a year ago. Last month, they got married.