TAMPA, Fla. — Mitt Romney reported owing $6.2 million in federal taxes on $42.5 million in income over the last two years, according to documents the Republican presidential contender’s campaign released Tuesday that play into the emerging debate over fairness in the tax code.

There were no major surprises in more than 500 pages of documents released under pressure after Romney’s defeat in Saturday’s South Carolina primary, where his lack of clarity about his taxes bothered voters.

Although Romney hasn’t filed his 2011 tax returns yet, the campaign estimated that the former Massachusetts governor made an estimated $20.9 million last year and said he expected to pay $3.2 million in taxes, a 15.4 percent rate. The documents also showed that Romney had offshore accounts in the Cayman Islands, and his blind trust had maintained a Swiss bank account until 2010.

It has long been known that Romney is wealthy, with an estimated net worth of $190 million to $250 million. What’s likely to raise questions, should he capture the Republican nomination, is the lower tax rate he pays since most of his income is derived from past investments rather than ordinary wages.

Romney’s tax returns contrast with those of his chief rival, Newt Gingrich, who reported income of about $3.16 million in his 2010 federal tax form, filed jointly with his wife, Callista. After deductions, the Gingrich family had an effective tax rate of 31.6 percent.

President Barack Obama, who was expected to use his State of the Union address Tuesday night to hammer away at the theme of fairness in the tax code, paid taxes at a 26 percent rate, according to his 2010 return.

By contrast, Mitt and Ann Romney reported income above $21.6 million in 2010, paid about $3 million in taxes and donated about $2.9 million. But because almost all their income came from past investments and was taxed as capital gains, the Romney family had an effective 2010 rate of taxation of about 13.9 percent.

“The numbers were all bigger than I was led to believe … but the return looks like what you’d expect,” said Roberton Williams, a senior fellow at the Tax Policy Center, a nonpartisan research center run by the Urban Institute and the Brookings Institution. “On the other hand, his income from working still seems pretty big, from speaker’s fees and other things” claimed on self-employment tax forms.

Among the gaffes Romney made while he campaigned in South Carolina was his declaration that he didn’t make much money from speaker’s fees. He was correct when it’s seen as a percentage of his income, but for most Americans, his $374,000 in such fees is a lot of money.

The lion’s share of Romney’s income is derived from investments, taxed at 15 percent. Ordinary income from wages can be taxed as high as 35 percent. Before the George W. Bush-era tax cuts in 2001 and 2003, the maximum tax bracket stood at 39.6 percent.

The Bush-era cuts are set to expire at the end of this year. Whether to let that happen is sure to be a major campaign issue.

For several years, Obama has proposed raising the taxes of individuals with taxable income above $200,000, saying the top earners should pay more to meet their fair share. Romney and other Republicans, however, favor making the Bush-era tax cuts permanent to encourage investment. The debate occurs as numerous studies show a widening wealth gap in America between the rich and everyone else.

“The bigger question is what kind of tax system do we want to have,” Williams said. “Very clearly Romney is paying a lot less than people who have income like his … high-paid CEOs are likely to have a higher tax rate.”

At Monday night’s Republican candidate debate in Tampa, Romney called his tax liability “entirely legal and fair.”

He added: “I pay all the taxes that are legally required and not a dollar more. I don’t think you want someone as the candidate for president who pays more taxes than he owes.”

To boost his case, Romney released a statement of support Tuesday from Fred Goldberg, who was the Internal Revenue Service commissioner under President George H.W. Bush.

“These returns reflect the complexity of our tax laws and the types of investment activity that I would anticipate for persons in their circumstances,” Goldberg said, speaking of the Romneys. “There is no indication or suggestion of any tax-motivated or aggressive tax planning activities. In my judgment, they have fully satisfied their responsibilities as taxpayers.”