Updated

With the frontrunners in the Republican presidential race suddenly battling for the mantle of transparency, Newt Gingrich is starting to lift the shroud from his personal financial dealings.

Until now -- amid persistent questions about the roughly $1.6 million that Gingrich's companies earned as a consultant to embattled mortgage giant Freddie Mac, over eight years' time -- relatively little has been disclosed about what the campaign calls "the various small businesses" the GOP presidential candidate had started since resigning as House speaker.

Gingrich began to shed light on the source of his wealth over the last week, with the release of his 2010 tax returns and documents pertaining to his Freddie Mac contracts.

The tax returns show Gingrich made more than $3.1 million in 2010, with more than $2.5 million of that coming from income from various partnerships and companies. He and his wife also took in more than $41,000 in speaking fees and board of director fees as well as less than $7,000 in rental income.

Among the partnerships and corporations that fuel Gingrich's income is Gingrich Holdings.

A campaign aide told Fox News that since January 1999, Gingrich has started a total of four companies, three of which were subsumed under Gingrich Holdings. Those three companies were the Gingrich Group -- the consulting firm whose clients included Freddie Mac, IBM, Microsoft and the U.S. Chamber of Commerce, among others -- Gingrich Communications and Gingrich Productions, the most recent start-up, incorporated in 2007. The latter firms were designed to absorb the income from the former speaker's books, documentaries and lecture tours.

The fourth firm Gingrich started, in 2004, was called the Center for Health Transformations, a for-profit "think tank" aimed at developing free-market solutions to intractable health care issues.

Details about the Gingrich Group's work began to come to light with the release of documents pertaining to the Freddie Mac contracts.

The campaign released a 2006 contract showing the firm was paid a monthly retainer fee of $25,000, adding up to $300,000 for the length of the contract. The campaign also released details of a 1999-2000 contract, which likewise included a $25,000-a-month retainer.

Gingrich has used these documents to rebut charges from Mitt Romney's campaign that he was effectively Freddie Mac's "chief lobbyist."

One passage from the 1999-2000 contract stated "nothing herein is or shall be construed as an agreement to provide lobbying services of any kind or engaging in lobbying activities." The statement went on to say the Gingrich Group would not provide lobbying services on Freddie Mac's behalf.

The campaign stressed that Gingrich himself was only a 60 percent owner of the Gingrich Group, which is privately held. The remaining shares were held by undisclosed business partners of the former speaker. As a result of that arrangement, the campaign said, Gingrich himself did not receive all of the fees associated with Freddie Mac or any of the group's other clients; rather, those funds went back into the business to pay salaries, overhead, etc.

The campaign says the candidate spent much of last winter, a year ago, consolidating the three "Gingrich" firms and the parent company, Gingrich Holdings, into one, new concern: Gingrich Productions, which presently employs "about a dozen" people, and of which Gingrich is the sole owner. All told, the campaign estimates that Gingrich's various businesses have employed a total of "hundreds" of individuals over the last 13 years, with "maybe 50" being the top number employed by any one company at any one time.

Collectively, the campaign estimates that the Gingrich small businesses averaged gross receipts of anywhere from $10 million to $20 million per year, and that the candidate's own personal wealth, as reflected in Federal Election Commission filings, stands at between $5 million and $20 million.

Fox News' James Rosen contributed to this report.

Editor's Note: An earlier version of this story ran in the Fox News Insider on Nov. 17, 2011.