Which one of the following is the oldest oil refinery in India?

Digboi is the oldest oil refinery in India and Asia. It was commissioned in 1901 in the Tinsukia district of Assam [c2][t2][t3]. The refinery was established following the discovery of oil in the region in the late 1880s and was initially operated by the Assam Oil Company [t2][t6]. In contrast, the other options were established much later: the Koyali refinery (Gujarat Refinery) was commissioned in 1965 [c2][t2], the Haldia refinery in West Bengal began operations in 1975 [c2], and the Mathura refinery in Uttar Pradesh was commissioned in 1982 [c3]. Digboi remains one of the oldest operating refineries in the world and is currently managed by the Indian Oil Corporation Limited (IOCL) [c1][t1][t10]. Its historical significance is marked by the legendary command 'Dig, boy, dig!' which gave the town its name [t6].

Sources

1. [1] Geography of India ,Majid Husain, (McGrawHill 9th ed.) > Chapter 8: Energy Resources > 3. The Brahmaputra Valley > p. 13
2. [2] Geography of India ,Majid Husain, (McGrawHill 9th ed.) > Chapter 8: Energy Resources > India: Refineries and their Production Capacity > p. 15
3. [3] Geography of India ,Majid Husain, (McGrawHill 9th ed.) > Chapter 8: Energy Resources > India: Refineries and their Production Capacity > p. 16
4. [4] https://en.wikipedia.org/wiki/List_of_oil_refineries_in_India