Tests performed on three different configurations of hybrid vehicles establish that significant quantities of on-board petroleum fuel can be conserved by allowing the batteries to be discharged during the driving mission. The depleted batteries are then charged when the vehicle is not in use. Savings of as much as 50% of the on-board petroleum have been experienced with tests on the FDC. On SAE J227a, gasoline FE greater than 50 mpg was measured.Part of the energy for driving is thus transferred from on-board petroleum to off-board electricity generated from coal, hydro-electric or nuclear power plants, with no sacrifice in vehicle performance. The total energy used, when considering the replacement of energy to recharge the batteries, is analyzed. The results are favorable for the hybrid.A recommended new driving cycle for testing hybrids is discussed briefly.