Male drivers for Uber Technologies Inc. earn about 7 percent more than their female counterparts, according to a collaborative study taken by the company, the University of Chicago and Stanford University.

The study, which measured some 1.8 million trips over two years, found that women earn $1.24-per-hour less than men, and $130 less than men for an entire week on average in the U.S..

The results may sound unusual, since gender doesn’t come into the equation when rides are assigned to drivers, so the hourly rate would be expected to be more or less equal. There are no driver-client negotiations, and the cost of the trip is decided by a gender-blind algorithm.

“Our research also finds that both average rider ratings of drivers and cancellation rates are roughly equivalent between genders and we find no evidence that outright discrimination, either by the app or by riders, is driving the gender earnings gap,” Uber wrote in a blog post Tuesday.

Rather than a matter of discrimination, it seems the gap is about driver behavior. The study picked up on three main points as to why there is some pay disparity.

One is that men tend to driver faster, by only 2 percent, so they make more trips. Another factor is that male drivers tend to stick with Uber longer, so their experience leads to knowing which route and times pay more. Lastly, it seems men work more during hours when fares are higher, such as during surge-pricing periods and throughout the night.

Freakonomics interviewed three of the researchers involved with the study and explained the reasons for the pay disparity in more detail.

“When you analyze the mounds and mounds of data, it ends up that we have a 7 percent difference,” said John List of the University of Chicago. “Now, what’s interesting and intriguing is that after you unpack those differences, what you find is that there are perfectly reasonable explanations for what’s happening on the Uber platform.”

The researchers said that perhaps there are certain constraints on women in life that prevent them from working more hours and doing more trips, but it might also just be a preference. As it stands, it seems the pay gap isn’t actually the result of discrimination.

Image: Jason Tester via Flickr