The small town of Digboi in the remote north eastern corner of the country is the birth place of the Oil Industry in India. Digboi Refinery, commissioned on 11 December 1901, is India's oldest operating refinery and one of the oldest operating refineries in the world.

The historic Digboi Refinery has been termed as the "Gangotri of the Indian Hydrocarbon sector".

Earlier owned and operated by the Assam Oil Company Limited / Burmah Oil Company, it came into the fold of the Indian Oil Corporation Limited by an Act of Parliament on 14 October 1981 and became the Assam Oil Division of Indian Oil Corporation Limited.

Digboi Refinery has crude processing capacity of 0.65 MMTPA. It processes waxy crude extracted from oil fields operating in area nearby Digboi. It has also started processing of Crude condensate in 2018.

Digboi Refinery was modernized with commissioning of new CDU, DCU, CRU towards end of 1990s. In early years of 21st century, new units SDU, WHFU, HDTU, HGU, SRU and Captive Power Plant were commissioned. Later on, Digboi Refinery commissioned MSQU units NHT and ISOM units in 2010. The refinery also has Wax Moulding unit and Wax Pelletisation unit for production of finished Wax in Slab and Pellet form respectively. It has also installed and commissioned a CRMB+ unit in 2018 for production of Crumb Rubber Modified Bitumen using IOCL-R&D developed technology.

Digboi Refinery's current product portfolio includes LPG, BS-IV compliant MS & HSD, Fuel Oil, Wax, RPC and Sulfur.