A loose ring, the inner surface of which rides a shaft or journal and dips into a reservoir of lubricant from which it carries the lubricant to the top of a bearing by its rotation with the shaft.

Oil in a reservoir underlying a gas-cap. In a reservoir on an anticlinal structure with a large gas-cap the center of the field area may consist only of gas wells with a ring of oil wells surrounding the gas producing area, hence the term oil ring.

Piston ring that scrapes oil from the cylinder wall to control cylinder wall lubrication and prevent excessive oil loss past the piston and into the combustion chamber.