This study emphasizes the value and huge potential savings that can be attained by harmonizing some of the inherent differences between the Fuel Efficiency and Mass (light-weighting) regulations prevalent in the USA, EU and China. The definitions and intricate nuances of FE and Mass regulations for the three regions have been illustrated and compared. In particular, the nuances of footprint-based and mass-based light-weighting regulations have been discussed. We highlight that there is no value in trying to lightweight vehicles if their mass is hitting the ceiling of a test-weight-class. It only reduces the fuel consumption and GHG emissions of the vehicle but, not the CO2 emissions ‘target’. The effect of light-weighting an LCV (light commercial vehicle) within a test-weight class is illustrated in detail. The signatures of drive cycles used for certifying vehicles in the three regions are presented. A typical vehicle’s FE performance sensitivity to a 10% change in mass, on the standard regional drive cycles, is illustrated. In summary, the incentives of an OEM to treat mass differently in the three regions are discussed. A comparison of the regulatory and physical intricacies of the mass rules in the three regions is analyzed from various aspects, where we highlight the technical and financial challenges of an auto manufacturer when tailoring passenger cars to the region-specific regulations.