In which state is the oldest oil field of India?

Digboi is known as the Oil City of Assam where the first oil well in Asia was drilled. The first refinery was started here as early as 1901 by Assam Oil Company Ltd. Digboi has the oldest oil well in operation. The Indian Oil Corporation Ltd (IOC) took over the refinery and marketing management of Assam Oil Company Ltd. with effect from 1981 and created a separate division.