The largest U.S.-based companies added $206 billion to their stockpiles of offshore profits last year, parking earnings in low-tax countries until Congress gives them a reason not to.

The multinational companies have accumulated $1.95 trillion outside the U.S., up 11.8 percent from a year earlier, according to securities filings from 307 corporations reviewed by Bloomberg News. Three U.S.-based companies — Microsoft Corp., Apple Inc. and International Business Machines Corp. — added $37.5 billion, or 18.2 percent of the total increase.

"The loopholes in our tax code right now give such a big reward to companies that use gimmicks to make it look like they earn their profits offshore," said Dan Smith, a tax and budget advocate at the U.S. Public Interest Research Group, which seeks to counteract corporate influence.