Republican front runner Rick Santorum released his 2007-10 tax returns on Wednesday night. 

His returns show that the former Pennsylvania senator  has paid tax at effective rates between 25.4 percent to 28.5 percent in the four years.

The tax returns, first published by Politico, clearly indicate that Santorum's fortunes have increased after he left the Senate in 2006.

The adjusted gross income of Santorum and his wife was $659,637 in 2007 and it went up to $ 945,100 in 2008. In 2009, their income crossed the one million mark ($1.1 Million) and in 2010 it slipped to $923,411.  

The tax returns have also thrown some light into Santorum's wealth sources and the pattern of his wealth growth. As he disclosed earlier, most of their wealth comes from consulting fees and media appearances and not from capital gains and dividends.

At the same time, tax returns show that his wealth has started increasing during his Senate days and the after the Senate years. This might be an indication that though he has not projected himself as a lobbyist, yet he is not exactly the Washington outsider.

According to an AP analysis, His newfound affluence reflects his close ties to Washington's business and lobbying circles during his 12 years in the Senate and his smooth transition into their world after he left office.

The tax returns of the GOP candidates had become a hot issue in the presidential race after Mitt Romney refused to disclose his returns. Four years' return is the highest any GOP presidential candidates have released in this election cycle. Santorum's tax returns show that his rates are much greater than Mitt Romney's tax rates, but less than that of Newt Gingrich.