Although it always had hundreds of competitors, Standard Oil gradually gained dominance of oil refining and sales as market share in the United States through horizontal integration, ending up with about 90% of the US market.[53] In the kerosene industry, the company replaced the old distribution system with its own vertical system. It supplied kerosene by tank cars that brought the fuel to local markets, and tank wagons then delivered to retail customers, thus bypassing the existing network of wholesale jobbers.[71] Despite improving the quality and availability of kerosene products while greatly reducing their cost to the public (the price of kerosene dropped by nearly 80% over the life of the company), Standard Oil's business practices created intense controversy. Standard's most potent weapons against competitors were underselling, differential pricing, and secret transportation rebates.[72]
The firm was attacked by journalists and politicians throughout its existence, in part for these monopolistic methods, giving momentum to the antitrust movement. In 1879, the New York State Legislature's Hepburn Committee investigations into "alleged abuses" committed by the railroads uncovered the fact that Standard Oil was receiving substantial freight rebates on all of the oil it was transporting by railroad—and was crushing Standard's competitors thereby.[73] By 1880, according to the New York World, Standard Oil was "the most cruel, impudent, pitiless, and grasping monopoly that ever fastened upon a country". To critics, Rockefeller replied, "In a business so large as ours ... some things are likely to be done which we cannot approve. We correct them as soon as they come to our knowledge."[74]