In recent years, automobile manufacturers have been producing gasoline-powered vehicles that have very low tailpipe and evaporative emissions in order to meet very stringent certification standards set by the U.S. Environmental Protection Agency and the California Air Resources Board. These extremely low emitting vehicles are 98% to 99% cleaner than catalyst-equipped vehicles produced in the mid 1980s. To better understand the emission characteristics of these extremely low emitting vehicles as well as their potential impact on future air quality, researchers at the University of California, Riverside have conducted a comprehensive study consisting of: 1) an emission measurement program; 2) the development of specific emission models; and 3) the application of future emission inventories to air quality models. Results have shown that in nearly all cases, these vehicles have emissions that are well below their stringent certification standards and continue to have low emissions as they age. Based on the measurement results, new modal emission models have been created for both ULEV- and PZEVcertified vehicles. The model results compare very well to actual measurements. With these models, it is possible to accurately predict future mobile source emission inventories that will have an increasing number of these extremely low emitting vehicles in the overall vehicle population. It is expected that a large penetration of these vehicles in the vehicle fleet will have a significant role in meeting ozone attainment in many regions.