While Warren Buffett has generated attention with his complaints that he and his fellow billionaires pay federal income taxes at a lower rate than his secretary — about 17 percent — the real figure is often smaller, said David S. Miller, former chair of the tax section of the New York State Bar Association and a partner at Cadwalader, Wickersham & Taft LLP in New York.

“The problem is not that people like Warren Buffett pay tax at a 17 percent rate, it's that they can use complex transactions not available to most Americans to get cash from their appreciated stock without paying any taxes at all,” Miller said.

The rate at which the 400 U.S. taxpayers with the highest adjusted gross income actually paid federal income taxes –their so-called effective tax rate — fell to about 18 percent in 2008 from almost 30 percent in 1995, IRS data show. That's the tip of the iceberg, since much of their wealth never converts into income on a tax return, McCaffery said.

In the McCombs case, the billionaire entered into transactions known as variable prepaid forward contracts. He received about $259 million for lending an investment bank his Clear Channel shares with a promise to deliver the stock for good a few years later. The arrangement enabled McCombs to defer paying capital gains tax because he hadn't sold his shares, lawyers for the billionaire said. The IRS deemed the transaction a sale since the bank paid McCombs cash and got the use of his stock almost immediately.

Transactions like these may complicate plans by U.S. President Barack Obama to help close the federal deficit by increasing taxes on millionaires. Obama has said the tax code should contain a “Buffett Rule” to ensure that millionaires pay taxes at least at the same rate as middle-class Americans. Republicans have said they prefer lowering tax rates for businesses and the wealthy. Buffett declined to comment.

In the past two years, some of the wealthiest executives in the U.S. have used deals similar to McCombs's to reap returns while deferring the taxes without running afoul of IRS rules, securities filings show.

Dole Food Co. Chairman David H. Murdock received about $228.6 million in 2009 against his Dole shares — tax-free until he is scheduled to deliver shares in November 2012, a filing shows.

Starr International Co., the investment vehicle run by Maurice “Hank” Greenberg — forced from his position as chairman and chief executive officer of American International Group Inc. in 2005 — utilized a prepaid forward agreement last year to receive $278.2 million from an investment bank, according to a March 2010 regulatory filing. The investment vehicle isn't slated to deliver the AIG stock until 2013.

Lauder received $72.9 million in June as part of a variable prepaid forward sale and is scheduled to deliver the Estee Lauder Cos. shares in June 2014, according to a filing with the U.S. Securities and Exchange Commission.

Spokespersons for Lauder, Murdock and Starr International declined to comment.

While the tax treatment of these plans isn't disclosed in the filings, “there's no other reason to enter into such a convoluted arrangement,” said Robert Willens, an independent tax accounting analyst in New York. These arrangements can cost several million dollars in fees, according to tax planners.

Taxes on capital gains are triggered when assets like appreciated shares are sold — a process called realization. What constitutes a realized, taxable sale is a frequent bone of contention between the IRS and the clients of tax planners.

Transactions intended to pull cash out of appreciated assets tax-free aren't limited to stock. Boston real estate developer Arthur M. Winn exited his interest in a piece of real estate by converting his stake into a share of a partnership free of any capital gains tax, court filings show.

The IRS objected and claimed Winn and his partner should have reported a $12 million taxable gain. A U.S. Tax Court judge sided with Winn on one aspect of the deal; others were settled with the government. The details haven't been disclosed.

Winn, who earlier this month pleaded guilty to making illegal campaign contributions, has retired from WinnCompanies. He did not respond to messages left with his attorney and with the company.

Miller, the former chair of the tax section of the New York State Bar Association, has proposed a so-called mark-to-market system to tax the annual appreciation in the stock holdings of the top 1/10th of 1 percent of taxpayers. That would essentially tax gains in a given year regardless of whether the shares are sold. In a 2005 article in the journal Tax Notes he estimated this approach would raise between $490 billion and $750 billion over a decade.

Borrowing against appreciated stock and real estate is a popular tax deferral strategy particularly as interest rates plummet, said Randy Beeman, a private wealth manager at The Wise Investor Group in Reston, Virginia, a unit of Robert W. Baird & Co. The interest rate on loans to some wealthy individuals has hovered around 1 percent.

McCombs, ranked 312 on the most recent Forbes 400 list of the richest Americans, made his fortune in automobiles, real estate, and then by building Clear Channel into a large radio station operator and outdoor advertising business. He is now the chairman of Xe Services LLC, the military security contractor formerly called Blackwater Worldwide.

In the late 1990s, McCombs borrowed about $300 million to finance the purchase of the National Football League's Minnesota Vikings. By 2002, the Clear Channel shares pledged as collateral were falling in value and McCombs faced margin calls from lenders. He didn't want to sell his shares, partly because of “a strong emotional attachment to his ownership in the company,” according to a filing by his lawyers in U.S. Tax Court.

Instead, he entered into a series of variable prepaid forward contracts, receiving about $259 million from JPMorgan Chase & Co. in exchange for an agreement to deliver his Clear Channel stock in one to three years. The transaction was structured to limit his potential losses by varying how many shares he would deliver at the end of the transaction.

He loaned those shares to JPMorgan in the interim. That allowed the New York-based bank to short the stock — selling the borrowed shares to hedge against any decline in the price of the stock it would eventually receive from McCombs.

Lawyers said the cash received up front didn't have to be reported as income because it wasn't a taxable sale until McCombs turned over those shares for good.

The IRS said the transaction was a cash sale of the shares, generating taxable income of as much as $213 million.

Over the years, the IRS has tried to crack down on such deals. In 2006, the agency declared that including a share loan meant these types of transactions were sales, triggering an immediate income tax obligation. In McCombs's case, his lawyers contended that the share loan was separate from the first part of the transaction, and thus didn't transfer the so-called “benefits and burdens” of owning the stock. He settled his case for $23 million in back taxes plus interest.

In 2010, a U.S. Tax Court judge found Philip Anschutz, the entertainment, oil and media investor, owed $94 million in taxes after he used transactions similar to the ones used by McCombs. Anschutz, identified by Forbes as the 39th richest man in the U.S., is appealing the decision.

“The IRS shifted its view and threatened a legitimate business practice and that will have a dampening effect on investment,” said a spokesman for Anschutz.

The IRS has “gotten more hostile toward these transactions over the years,” through its various technical pronouncements and litigation, said Willens, the accounting analyst. Since 2006, such transactions haven't included the interim loan of shares to the investment bank, he said.

“It's still desirable to defer the tax and wind up with an interest free loan from the government,” he said. “Chances are you don't get audited and if it does get challenged the odds are good you'll have a settlement for some fraction of the amount you saved. Who wouldn't want that?”

Bloomberg