John D. Rockefeller had bought out the…

John D. Rockefeller had bought out the Clark brothers for $72,500 at auction and established the firm of Rockefeller & Andrews in  February 1865, in what will later be described by oil industry historian Daniel Yergin as a "critical" action. (Yergin, Daniel. The Prize: The Epic Quest for Oil, Money, and Power. New York: Simon & Schuster, 1991.)

Rockefeller is well-positioned to take advantage of the coming postwar prosperity and the great expansion westward, fostered by the growth of railroads and an oil-fueled economy.

He borrows heavily, reinvests profits, adapts rapidly to changing markets, and fields observers to track the quickly expanding industry.

In 1866, his brother William Rockefeller builds another refinery in Cleveland and brings John into the partnership.