Some economic historians have observed that Standard Oil was in the process of losing its monopoly at the time of its breakup in 1911. Although Standard had 90 percent of American refining capacity in 1880, by 1911 that had shrunk to between 60 and 65 percent, due to the expansion in capacity by competitors. Numerous regional competitors (such as Pure Oil in the East, Texaco and Gulf Oil in the Gulf Coast, Cities Service Company and Sun Oil in the Midcontinent, Union Oil in California, and Royal Dutch Shell overseas) had organized themselves into competitive vertically integrated oil companies, the industry structure pioneered years earlier by Standard itself. In addition, demand for petroleum products was increasing more rapidly than the ability of Standard to expand. The result was that although in 1911 Standard still controlled most production in the older regions of the Appalachian Basin (78 percent share, down from 92 percent in 1880), Lima-Indiana (90 percent, down from 95 percent in 1906), and the Illinois Basin (83 percent, down from 100 percent in 1906), its share was much lower in the rapidly expanding new regions that would dominate U.S. oil production in the 20th century. In 1911 Standard controlled only 44 percent of production in the Midcontinent, 29 percent in California, and 10 percent on the Gulf Coast.
Question: In which area did Standard's percent share drop the most by 1911?
Answer: Illinois Basin