The Digboi Refinery was set up at Digboi in 1901 by Assam Oil Company Ltd.. 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. This division has both refinery and marketing operations. The refinery at Digboi had an installed capacity 0.50 MMTPA (million metric tonnes per annum). The refining capacity of the refinery was increased to 0.65 MMTPA by modernization of refinery in July, 1996. A new delayed Coking Unit of 1,70,000 TPA capacity was commissioned in 1999. A new Solvent Dewaxing Unit for maximizing production of microcrystalline wax was installed and commissioned in 2003. The refinery has also installed Hydrotreater to improve the quality of diesel.