In June 1870, Flagler and Rockefeller formed Standard Oil of Ohio, which rapidly became the most profitable refiner in Ohio. Standard Oil grew 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 in collusion with Standard and other oil men outside the main oil centers. The cartel received preferential treatment as a high-volume shipper, which included not just steep rebates of up to 50% for their 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 from independent oil well owners, including boycotts and vandalism, which eventually led to the discovery of Standard Oil's part in the deal. A major New York refiner, Charles Pratt and Company, headed by Charles Pratt and Henry H. Rogers, led the opposition to this plan, and railroads soon backed off. Pennsylvania revoked the cartel's charter, and non-preferential rates were restored for the time being.