A zero turning radius mower oil extension kit includes a supplemental oil tank that may be installed under a wet sump of a zero turning radius mower engine. A plurality of conduits may be installed between the supplemental oil tank and at least one drain port of the engine for continuously circulating a volume of oil between the supplemental oil tank and the wet sump of the engine while the engine is running. The kit extends the time between oil changes because of the increased volume of oil in the supplemental oil tank and the wet sump.