is a system of lubrication in which the lubricant is supplied to the lubricated part at a minimal rate and is not returned or recirculated. Lubrication by oil can, mechanical lubricator, centralized grease system, lubricating device, oil mist, etc., is done on a once-through basis. Since the lubricant is not recovered, high oxidation stability and long service life are usually not necessary, but viscosity and other properties may be very important. Oils that meet the moderate requirements of once-through lubrication are known variously as machine oils and general-purpose oils.

Also see centralized lubrication, chain oil, cylinder oil, oiler, oil mist lubrication.