What is the relationship between Bharat Petroleum and Petroleum in the context of the input sentence. Choose an answer from: product/material produced; manufacturer; distributed by; industry; position held; original broadcaster; owned by; founded by; distribution format; headquarters location; stock exchange; currency; parent organization; chief executive officer; director/manager; owner of; operator; member of; employer; chairperson; platform; subsidiary; legal form; publisher; developer; brand; business division; location of formation; creator.

State-owned fuel retailers -- IOC, Bharat Petroleum Corp (BPCL) and Hindustan Petroleum Corp (HPCL) -- revise petrol and diesel prices on 1st and 16th of every month based on average imported cost and rupee-dollar exchange rate in the previous fortnight.

Answer: product_or_material_produced