The most difficult aspect in enforcing Section 1 of the Sherman Act has been to prove tacit or informal collusion. Sometimes the case was clear-cut. For example, in 1936, the U.S. Engineer’s office received 11 closed bids to supply 6,000 barrels of cement, each quoting a price of $3.286854 per barre! The probability of identical prices, down to the sixth decimal, occurring without some from of collusion is practically zero. One of the most important collusive agreements uncovered and successfully prosecuted was the “electrical machinery conspiracy “ in which General Electris, Westinghouse, and a number of smaller companies producing electrical, equipment pleaded guilty in 1961 to violation of antitrust laws for price fixing and had to pay over $400 million in damagers to customers in civil suits, 7 of their executives were sent to jail, and 23 others received suspended sentences.