Base oils, are one of the specialty products produced by a refinery.

Base oils are not a fuel. They are blend stocks used to formulate a variety of lubricating oils for use in engines and other machinery.

Base oils are produced by extracting and treating high viscosity material from narrow distillation cuts of vacuum gasoil or vacuum resid. This requires special processing through a number of different units comprising the lubes plant.

Producing base oil is typically very profitable for a refinery because it allows the refiner to take some of the lowest valued part of crude oil, vacuum gasoil or vacuum resid, and sell it as a high-valued specialty product, but base oil production facilities are a relatively high capital cost per barrel so only a subset of refiners have installed them.