About 9,000 U.S. taxpayers have each accumulated at least $5 million in individual retirement accounts, said the Government Accountability Office, raising questions about some investors’ tax-advantaged returns.

The preliminary report attaches data to an issue that drew attention during the 2012 presidential campaign, when Republican nominee Mitt Romney reported an IRA worth $20 million to $102 million.

Senate Finance Committee Chairman Ron Wyden said many of these “massive” accounts come from deals available only to executives who can quickly turn “dirt cheap” stocks into gold.

“The IRA was never intended to be a tax shelter for millionaires,” Wyden, an Oregon Democrat, said at a hearing today in Washington. “With limited resources, it’s crucial to use taxpayer dollars as wisely as possible.”

Today’s GAO report said someone who contributed the maximum amount each year to an IRA from 1975 to 2011 and invested it in the Standard & Poor’s 500 Index would have about $350,000. The maximum contribution this year is $5,500, plus an extra $1,000 for people age 50 and older.

The total amount could be as much as $4 million per person, though, for people who rolled over 401(k)-style accounts or used the higher IRA contribution limits available to self-employed taxpayers.

‘Aggressive’ Investment

“Even assuming maximum contributions sustained over decades and rolled over from an employer plan,” the report said, “it would take an aggressive stock market investment strategy or investments in assets unavailable to most investors to accumulate an IRA balance over $5 million.”

Beyond that, there were an estimated 1,100 taxpayers with IRAs exceeding $10 million as of 2011, including about 314 with more than $25 million. About 99 percent of the 43 million taxpayers with IRAs have less than $1 million.

Romney, the co-founder of Bain Capital LLC, never explained how he had been able to accumulate so much wealth inside his IRA. One possibility is that he valued some Bain investments at low amounts when he contributed them before they boomed inside the IRA.

The broad ranges on financial-disclosure forms for political candidates make it difficult to tell exactly how rare Romney’s IRA is. Even at the $20 million low end of the estimate, it was in the top 0.003 percent of all IRAs.

In 2013, President Barack Obama proposed new limits on tax- advantaged retirement accounts, including IRAs and 401(k)-style plans. Under the plan, which hasn’t advanced in Congress, people wouldn’t be able to add tax-favored contributions once their combined account balances reached about $3.2 million.

The GAO report, released in conjunction with today’s Finance panel hearing on retirement policy, didn’t make any recommendations. A further report is expected later this year.