In January 1870, Rockefeller formed Standard Oil of Ohio, which rapidly became the most profitable refiner in Cleveland. When it was found that at least part of Standard Oil's cost advantage came from secret rebates from the railroads bringing oil into Cleveland, the competing refiners insisted on getting similar rebates, and the railroads quickly complied. By then, however, Standard Oil had grown to become one of the largest shippers of oil and kerosene in the country.
The railroads were fighting fiercely for traffic and, in an attempt to create a cartel to control freight rates, formed the South Improvement Company. Rockefeller agreed to support this cartel if they gave him preferential treatment as a high-volume shipper, which included not just steep rebates for his product, but also rebates for the shipment of competing products. Part of this scheme was the announcement of sharply increased freight charges. This touched off a firestorm of protest, which eventually led to the discovery of Standard Oil's part of the deal. Undeterred, Rockefeller continued with his self-reinforcing cycle of buying competing refiners, improving the efficiency of his operations, pressing for discounts on oil shipments, undercutting his competition, and buying them out. In less than two months in 1872, in what was later known as "The Cleveland Conquest", Standard Oil had absorbed 22 of its 26 Cleveland competitors. For many of his competitors, Rockefeller had merely to show them his books so they could see what they were up against, then make them a decent offer. If they refused his offer, he told them he would run them into bankruptcy, then cheaply buy up their assets at auction.