Innovation of Hybrid-Electrical Vehicles (HEV) has led to consumer demand for their fuel efficiency and emissions benefits among a growing segment of the population. An HEV is driven by a combination of an internal combustion engine and an electric motor. A distinguishing feature of the HEV is the ability to turn off the IC engine when the power available from the electrical system exceeds that required to propel the vehicle. This results in net cooler operating temperatures of the IC engine and more frequent starts of the engine.This research program was initiated to determine if the HEVs have any special lubrication requirements relative to those used in non-hybrid variety, and to look for opportunities to develop lubricant systems specifically tailored for such vehicles.In the first phase of this program, two hybrid vehicles in taxi service with high mileage accumulation, specifically a 2006 Toyota Prius with 400K odometer mileage and a 2009 Toyota Camry Hybrid with 264K odometer mileage, were inspected for signs of hardware distress or otherwise unusual features. In the next phase of this program, lubricants with varying rheological and performance properties were tested in a New York City fleet of 2012 Toyota Camry Hybrid taxis. Some of the observations from these inspections and used oil analysis will be discussed in the paper.