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Four light duty gasoline-electric hybrid vehicles (Toyota Prius, Honda Civic, Honda Insight and Ford Escape) were tested over five different driving cycles at two temperatures using chassis dynamometer emissions testing procedures. The vehicles were tested at 20 °C and -18 °C. Second-by-second gaseous emissions and total particle number emissions from the hybrid vehicles show patterns that are in some ways similar to conventional multiport fuel injected gasoline vehicles, with large increases in concentration on accelerations. Under driving conditions where the engine may be turned off and on, or under conditions where the electric drive assists in accelerations, different patterns are observed. These patterns can also differ from one repeat of a driving cycle to another, depending on the state of charge of the battery. Cold temperature operation is very demanding on the electric system of the hybrids. The batteries are challenged not only in starting the vehicle but in retaining charge during operation. These conditions result in much higher fuel consumption and mass emission rates of pollutants and greenhouse gases as compared to standard temperature operation and also greatly influence the transient nature of emissions from these vehicles.