For the first time, researchers have attempted to estimate the size of underground sex economies in eight major cities. According to the Urban Institute, Dallas' sex industry is worth about $99 million. The groundbreaking research on illicit economies also estimates the local gun and drug markets at $171 million and $191 million, respectively.

In addition to Dallas, the survey examined the underground sex economies in Atlanta, Denver, Kansas City, Miami, Seattle, San Diego and Washington D.C. Atlanta's underground sex trade brought in the most money at $290 million; Denver brought in the least, with about $40 million.

The survey created "scientifically rigorous estimates" for prostitution in 2003 and 2007. With the exception of Seattle and Atlanta, all the underground sex economies shrunk in that four-year period.

Researchers gleaned information from interviews with 73 convicted pimps and hundreds of law enforcement officials.

In Dallas, researchers interviewed 15 pimps, seven child pornographers and six sex workers. They also spoke with officials from the Dallas Police Department, Dallas FBI, Homeland Security and IRS.

Dallas pimps earn about $12,000 a week in cash, compared to more than $32,000 a week in Atlanta, but the survey revealed that pimps aren't the only ones profiting off prostitutes. Employees at hotels, cellphone stores, night clubs and car dealerships would often "turn a blind eye to prostitution," give discounts, or even tip off pimps to police investigations in exchange for cash or sexual favors.

The survey found that Dallas' sex economy is "mainly composed of pimp-controlled online and street-based sex trafficking and voluntary prostitution." There is also an increasing number of "erotic massage parlors." Researchers determined that Dallas' legitimate sexualized businesses, including massage parlors and topless bars, can serve as fronts for prostitution and sex trafficking.

"A practice relatively unique to Dallas is that non-Asian pimps run some massage parlors and send some of their women and girls to work in massage parlors owned and operated by Asians," the survey reads.

Like nearly every other business, the sex trade is increasingly an online transaction. Forty-nine percent of pimps reported using the Internet to attract business. Online classifieds, social media, discussion boards, chat rooms, dating websites and custom web pages were all cited as prime marketing tools.

The survey highlighted several avenues to combat the commercial sex industry, including increased intelligence sharing across law enforcement units, public awareness campaigns, and greater political will in the form of funding for mental health services and dedicated police units.

"The underground commercial sex economy is still unsettlingly murky, but by shining more light on it we can help more victims to escape the shadows," the survey reads.