When Tyson Foods Inc. and Wal-Mart Stores Inc. received internal reports that employees may have paid bribes in Mexico, each faced the same vexing question: should they turn themselves in to U.S. authorities?

Tyson, the biggest U.S. food processor, admitted bribing government-employed inspectors and paid $5.2 million to avoid prosecution. Wal-Mart, the world's largest retailer, began an internal probe in 2005, shut it down and didn't disclose the matter to regulators and prosecutors until late last year, after learning the New York Times was investigating, the paper said.

The U.S. offers leniency to companies like Tyson that self-report. Yet many choose to remain quiet, calculating that they will cooperate with the government if it uncovers their bribery. Companies root out their wrongdoing and improve their compliance programs, assuming that any credit the government gives them for self-reporting is not worth the fines and penalties and negative publicity that follow disclosure.