The oil fields of New York comprise some 50,000 acres. The most westerly pool of importance is in Cattaraugus County, and it is the northerly continuation of the Bradford pool of Pennsylvania. To the east in Allegany County is the Richburg pool, the largest and most productive in the state. Several smaller pools occur, among which is the Marsh Pool in Steuben County, the most easterly producing pool in the United States. The oil region of New York is a dissected plateau, as a result of which the main producing sand of Devonian age is found at depths varying from about 900 feet in the valleys to over 2,000 feet for the uplands. In spite of more than 15,000 wells that have been drilled into the oil sands, their structure is but imperfectly known. A general southwest dip is enerally recognized, and a few local anticlines and synclines have been determined, but undoubtedly many more are present. Another type of structure is the flat-top, basin-shaped sand lense. The absence of salt water from most parts of the fields and the presence of oil in synclines are noteworthy features. With no important areal expansion of the pools in twenty-five years the present production is greater than fifteen years ago. Increase in production is due largely to "flooding" or restored pressure from water wells.