The monopolization of the American petroleum industry by Standard Oil violated the Sherman Antitrust Act, and Standard Oil would be forced to break apart into smaller companies. This case established that antitrust law only bans "unreasonable" trade restraints. Decided May 15, 1911 (argued 1910). Opinion of the Court: White Topic: Businesses/Corporations/Contracts. Standard Oil Co. of New Jersey v. United States, 221 U.S. 1 (1911), was a landmark U.S. Supreme Court decision that ruled that John D. Rockefeller's petroleum conglomerate Standard Oil had illegally monopolized the American petroleum industry and ordered the company to break itself up. The decision also held, however, that U.S. antitrust law bans only "unreasonable" restraints on trade, an interpretation that came to be known as the "rule of reason". Wiki link