Step 1: Understanding Digboi.
Digboi is a town located in the Tinsukia district of Assam, India. It is often referred to as the "Oil City of Assam" because it houses one of the oldest oil refineries in the world.
Step 2: Identifying what Digboi is famous for.
The first oil well in Asia was drilled in Digboi in the late 19th century. Hence, the town is globally recognized for its petroleum industry.
Step 3: Conclusion.
Therefore, Digboi is famous for Petroleum.