The International Lubricant Standardization and Approval Committee (ILSAC) GF-2 specification requires Passenger Car Motor Oils to provide enhanced fuel economy in a modern low friction engine (ASTM Sequence VIA). The durability of this fuel economy improvement is becoming increasingly important and will be addressed in the successor to the Sequence VIA, the Sequence VIB, which proposed for ILSAC GF-3. Previous investigations have indicated that the choice of detergent system and friction modifier have a large impact on the fuel economy of a lubricant, and this study was designed to analyze these effects further. The work was carried out in three phases. In the first phase, seven detergent systems were evaluated and compared to currently available GF-2 lubricant in a vehicle equipped with a 4.6L SOHC V8 engine using a 500-mile Accelerated Mileage Accumulation (AMA) cycle. Fuel economy improvement was calculated against the ASTM Sequence VIA Baseline Calibration oil (BC-2) as a reference. In the second phase, a single detergent system was treated with four friction modifiers in a 4000-mile AMA accumulation with interim fuel economy testing at 500 miles to determine both initial fuel economy and durability of the systems. The final phase coupled the best detergent system/friction modifier and tested across five vehicle makes of differing engine displacement and valve train configuration to determine the general utility of the oil. In all three phases, fuel economy was measured using the EPA Federal Test Procedure and Highway Fuel Economy Test Cycles. The results of this investigation, including drain analyses, are discussed; and a comparison is presented of the three methods used in monitoring the fuel consumption: carbon balance, fuel flow metering, and gravimetric measurement.