A street prostitute in Dallas may make as little as $5 per sex act. But pimps can take in $33,000 a week in Atlanta, where the sex business brings in an estimated $290 million per year. It is not nearly as lucrative in Denver, where prostitution and other elements of an underground trade are worth about $40 million.

Those are some of the findings of a landmark government-sponsored report on the size and structure of the sex economy, including massage parlors, brothels and expensive escort services. The study also found that four in five pimps elect not to deal drugs and that little money trades hands in the child pornography business.

The report does not estimate the size of the illicit sex economy nationwide, instead analyzing the trade as of 2007 in eight cities: Miami, Dallas, Washington, Denver, San Diego, Seattle, Atlanta and Kansas City, Mo.

The report, commissioned by the Justice Department, is intended to address what researchers describe as wide gaps in the understanding of how the underground sex trade works, especially in the Internet age.