Big U.S. companies have lost billions buying their own stock.

Nearly half the companies in a study of the Standard and Poor's 500 index spent more on these buybacks than the shares are now worth. Combined paper losses from purchases in the past three years for these losers: $126 billion, or 15 percent of what they paid, according to an Associated Press study based on FactSet data.

The companies with five biggest paper losses:

— IBM: - $9.8 billion

—Qualcomm: -$7.4 billion

— American Express: -$4.1 billion

— Exxon Mobil: -$3.9 billion

— Hess: -$2.9 billion

— Chevron: -$2.8 billion