Current and proposed legislation regarding gaseous emissions has adversely affected the fuel economy of certain gasoline engines. Recent economic and environmental developments such as the fossil fuel shortage have improved the potential for the use of diesel engines as the power plant for small commercial vehicles and possibly certain passenger cars.Many variables affect fuel economy comparisons. Most of these variables can be associated with either the vehicle design or operation.The objectives of this paper are to relate fuel economy claims with a variety of cycles and to show how some of these claims can be justified. Also, to show how some of the more impressive diesel over gasoline economy claims relate more to the real world than comparisons based on EPA and SAE cycles.EPA originally started with one cycle and later split it into city and highway driving, to better cover the real world. SAE now has three cycles which represent a broader range of habits and requirements. There is still room for improvements at the low speed, short trip in cold weather, end of the scale. Also, the high volume of small Commercial vehicles such as Pick-Ups, Vans, Taxis, etc. need attention.To appreciate the significance of comparing the real world to SAE cycles, we must be familiar with “typical vehicle fuel economy as influenced by trip length” (1) *, “fuel savings potentials in short trip cold weather service” (2), and “other published statistics” (3) that have SAE level research and credibility.These papers show the results of surveys describing how up to 80% of trips and 50% of the auto fuel consumed are associated with trips of 10 miles or less.