I made a comment about this in the chess thread, but it had some wrong information and probably wasn't going to be seen so I wanted to make a post about it. Some of this is going to be copy and pasted from that comment. Some is going to be edited. It was in response to a statement about equal pay for equal work:

It really isn't equal work. Most ATP (men's tennis) and WTA (women's tennis) tournaments aren't held together. The Grand Slams are combined men and women's events. Like others have said, in these events men play Best of 5 and women play Best of 3, leading to a lot more tennis for the men. Furthermore, as a huge tennis fan, I've been to and seen a lot of tennis insider shit. These men take the game way way more seriously and work way way harder. Even the most popular female commentators like Martina Navratilova, Chris Evert, Lindsey Davenport know this and acknowledge it. It's completely anecdotal evidence but is very strongly supported anecdotal evidence. Now it would be impossible to judge how hard they're working and split the pay based on that, that would be silly. But the men, as a result of the much better product they put out (largely influenced by the harder work) and longer matches, make much more money for the sport of tennis. Contrary to what rshackleford141 suggested, this has always been the case and is even bigger today then in the past when women had great and popular players like Navritalova, Evert, Graf and Seles.

It would not be hard to split the pay difference roughly based on how much money each group is earning. I read an analysis of how much money ATP tournaments award players outside the mixed events compared to their WTA counterparts, which determined that ATP on average have a total prize money of $929,000 and WTA have a total prize money of $650,000. You can find that here. His study is pretty informal and is from 2006 thus it would be hard to check his numbers, but I'm going to do the same for 2012 and either edit this post or post it in the comments. The prize money reflects how much the tournament is earning from each separate product and would be decent starting point for determining how much the men are making for Grand Slams and how much the women are.

The same person in a different study broke down the total prize money per set for grand slams, and since obviously, women are playing less sets and getting equal money, the women are currently getting paid a sizable amount more for an equal amount of work on the court, and a smaller amount of work off the court. I couldn't find this study but it's obviously logical that equal pay, less work, means more pay for equal work.

I've seen the argument that since women are biologically disadvantaged in sports, they should get the handicap. Men are biologically disadvantaged in reproduction, where are our reproductive rights handicaps? Should we have more say on reproduction than women do because we're biologically disadvantaged? Absolutely not. And as it is now we get pretty much no say, so the biologically disadvantaged argument doesn't hold weight with me. And I know, reproduction and children are a hell of a lot more important than sports, which to me only says that if we were okay with handicaps based on a biological disadvantage, that one should get more attention and support than the sports one. But we all know it doesn't.

Sorry for the novel but I hope I've put the equal pay in tennis issue to rest for anyone who reads this.

Edit: I've run into somewhat of a stumbling block in my study. Took me about 20 tournaments to realize that the WTA websites only display Total Financial Commitment (TFC) while ATP websites list total prize money and TFC. TFC is the entire cost of running and operating the tournament including the prize money. I can compare each tournament's TFC but can't really do the total prize money. Also, I wanted to do a much more in depth analysis than the one I linked to, separating mixed events and not mixed events, displaying each tournament and noting noteworthy ones on a case by case basis, and other stuff, but my motivation went down when I realized I couldn't even get an accurate result with that. I might still do it anyway with the TFC, but for now I'm just going to do the same thing the study I linked to did, except with TFC. If you're interested in the more detailed results check back here in a while (a week maybe?) and if there is nothing else, PM me and I"ll let you know if I'm doing it or not.
Will fill this out once done.

Average TFC per tournament:

ATP: 109,246,000 U.S. dollars total for Men's, 63 tournaments = $1734070 per tournament.

WTA: 64,734,900 U.S. dollars total for Women's, 57 tournaments = $1135700 per tournament.

Sources: http://www.wtatennis.com/page/Calendar/0,,12781,00.html http://www.atpworldtour.com/Tournaments/Event-Calendar.aspx

Doesn't include the 3 remaining Grand Slams because the TFC for them has not yet been determined. They're mixed events though so it won't change the difference in total.

tl;dr Women in tennis are getting paid more for the same work on the court, and producing much less for the sport.