The Refinery is a civilian building and becomes available in the Industrial Age. It must be built within a city's economic radius and increases the overall production of Oil by 33%.
The effects of multiple Refineries stack, so two Refineries add 66% to the total base production, three Refineries add 99%, and so on. Oil production from rare resources (Rubber, Titanium and Uranium) is affected by the Refinery as well.
Unlike with the other production enhancing buildings, there are no technologies available for research at the Refinery.