Oil is a marketable item, and a processed material. It can be used in the maintenance of Military Units or Buildings to provide a attack or defense damage boost.
Players can obtain Oil by:
Producing 1x Oil in a company consumes 1 Petroleum and 1 Production Point.
A Military Unit's owner can use Oil to maintain their headquarters, for a hourly cost between 1 and 6 Oil per hour, depending on the headquarters' level.
Government members of a country can also use oil to maintain Buildings from a country's Regions: