Oil had been available in northwestern Pennsylvania since the earliest times. Around the time of the Civil War and the increased use of rail roads, however, entrepreneurs capitalized on Pennsylvania's natural resources. After E. L. Drake built the first successful oil well in Titusville, the industry boomed. D.O. Kelley worked at such a drilling operation in Oil Creek, PA prior to his enlistment in 1862. This May of 1861 letter to his sister details the beginning of the so-called "oil rush". Kelley writes: "I made $11.00 clear this week in cash there is an oil well here where I am that throws 1000 bbls of oil every day the gas that comes out remind me of an engine seaping steam it throws oil night and day…". The people here are also prosperous. "The people here are principally yankies. Some first rate men they think less of one dollar than the people in allegheny Co. of three cents but it is from the fact that money is so plenty they pay cash for everything…" After the war, many disenfranchised veterans came to Pennsylvania to try to strike it rich. Some did. Most of the latecomers, however, did not. The oil wells dried up quickly leaving many former soldiers bankrupt. D. O. Kelley might have been a millionaire if not for the intervention of the War Between The States. (One of Kelley's brothers Army friends ends up in the oil region in June of 1865.)