An overview description of candidate energy converters being considered for application in the Partnership for a New Generation of Vehicles (PNGV) program is presented. These energy converters include compression-ignition, direct-injection (CIDI) engines, gas turbine turbogenerators (T/G), and Stirling-cycle machines. Chrysler Corporation is investigating the CIDI engine for use in a parallel hybrid electric vehicle (HEV), Ford is investigating T/Gs, and General Motors is developing a Stirling-cycle generator for use in a series HEV. A summary of ongoing work for each of these technologies is provided, including current project status and future plans. An overview of current PNGV specifications for highly efficient energy converters is also included.