This study emphasizes the fact that there lies value and potential savings in harmonizing some of the inherent differences between the USA, EU, and China regulations with respect to the role of vehicle mass and lightweighting within Fuel Economy (FE) and Green House Gas (GHG) regulations. The definition and intricacies of FE and mass regulations for the three regions (USA, EU, and China) have been discussed and compared. In particular, the nuances of footprint-based, curb-mass-based, and stepped-mass-based regulations that lead to the differences have been discussed. Lightweighting is a customer benefit for fuel consumption, but in this work, we highlight cases where lightweighting, as a CO2 enabler, has incentives that do not align with rational customer values. A typical vehicle’s FE performance sensitivity to a change in mass on the standard regional certification drive cycles is simulated and compared across the three regions. 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. A proposed unified solution across the three regions could be a “Footprint-based regulation with certification mass assigned in a way that fully utilizes the benefits of lightweighting.