Digboi is a town and a town area committee in Tinsukia district in the north-eastern part of the state of Assam, India.The town's history begins in 1867 when a small group of men from the Assam Railway and Trading Co. found their elephants' legs soaked in black mud, that smelt somewhat like oil. The men began exploring more, and in 1889, the English started a small oil installation. India (and Asia) obtained its first refinery in Digboi in the year 1901. Various web sites offer variations on the elephant’s foot story, a consensus of which would be that engineers extending the Dibru-Sadiya railway line to Ledo for the Assam Railways and Trading Company (AR&TC) in 1882 were using elephants for haulage and noticed that the mud on one pachyderm’s feet smelled of oil. Retracing the trail of footprints, they found oil seeping to the surface. One of the engineers, the Englishman (not Canadian) Willie Leova Lake, was an ‘oil enthusiast’ and persuaded the company to drill a well.Oil India Ltd makes no reference to elephants’ feet in its company history,noting only that Lake noticed “the oil seepages around Borbhil”. Once the project had been approved, Lake assembled equipment, boilers, and local labour, and engaged elephants to haul the machinery to the site.
The first well was started in September 1889, but an encouraging first strike at 178 feet turned out to be a small pocket, and drilling recommenced. This continued until November 1890 when the well was completed at a total depth of 662 feet, and it was during this extended period of drilling that Oil India Ltd places Assam Oil Company was formed in 1899 to look after the running of the oil business in this area. 
The Digboi oil field produced close to 7,000barrels/day of crude oil at its peak, which was during World War II. The field was pushed to produce the maximum amount of oil with little regard to reservoir management; as a result, production started to drop almost immediately after the war. The current production from the Digboi fields is about 240 barrels/day. Over 1,000 wells have been drilled at Digboi – the first well in 1889 had stuck oil at 178 feet (54 m). In 1989, the Department of Posts, India came out with a stamp commemorating 100 years of the Digboi fields. The Digboi Refinery was commissioned in December'1901 and supplanted the earlier small refinery unit at Margherita. The Digboi refinery, commissioned in December'1901 is today India's oldest operating refinery. Over the 100 years it has undergone a transition from being an age old refinery to one with state-of-the-art technology comparable to any modern refinery.
When oil was discovered in remote Digboi there was no habitation in its immediate neighborhood. The jungle was dark and swampy. The forest was so thick and the undergrowth so dense that sunlight could never reach the ground. 
Once oil was found, the dense jungle made way for the growth of the oil industry in India. Over the past 100 years, Assam Oil and the petroleum industry of India with Digboi as its nucleus has been very much a part of this existing period. While looking back on the past with respect and to the future with confidence, we portray here how Digboi Refinery was successful in meeting the needs and challenges of the times, and how Digboi Refinery played a role in shaping and developing history over the past 100 years.
Digboi is now Headquarter of Assam Oil Division of Indian Oil Corporation Limited. The Earliest recorded to the existence of oil in India is found in the memories and dispatches of the Army Officers who penetrated the jungles of Upper Assam since 1825. 
Lt. R. Wilcox, Major A. White, Capt. Francis Jenkins, Capt. P.S. Hanney -- they all saw at different times petroleum exuding from banks of the Dihing River. Mr. C.A. Bruce (1828) and Mr. H.B. Medicott (1865) of the Geological Survey of India also saw oil while prospecting for coal in Upper Assam.
Today, though the crude production is not high, Digboi has the distinction of being the world’s oldest continuously producing oilfield. Digboi refinery, now a division of Indian Oil Corporation, had a capacity of about 0.65 MMTPA as of 2003. The Digboi refinery is the world's oldest oil refinery still in operation.With development in technology and infrastructure, Assam Oil Division is moving towards attaining higher standards of excellence. 
With a name that has existed for over 100 years, ready to meet the challanges of the future with its greatest resource - a committed and talented workforce. Assam Oil Division has always upheld its commitment towards the community at large, as a good corporate citizen. It has been carrying out various developmental activities in the region. In its journey forward it belives in carrying along with it, the community with which it co-exists. 
Today with its modern technology and facilities, Digboi Refinery produces major petroleum products like fuels, wax, bitumen and range of specialty products. This hundred year old Digboi refinery can very well be said a technical marvel of the past and present.