Standard Oil was never a literal monopoly, there was always some competition. They had about 90% of the market at their peak, and it was down to about 70% when

Standard Oil was never a literal monopoly, there was always some competition. They had about 90% of the market at their peak, and it was down to about 70% when they were broken up. True monopolies, e.g. Bell Telephone, local cable franchises, utilities, etc. are (almost?) always granted by the government.