There are problems predicted in meeting the future demands for diesel fuel of conventional quality in Canada. One possibility for extending supplies is to add virgin naphthas to the normal diesel fuel blends. Broad-cut fuels of different volatilities have been evaluated in two passenger car diesel engines in chassis dynamometer and road tests and also checked for cold-starting capability and exhaust emissions. With some restrictions on volatility for high-temperature operation and in cetane number for low-temperature driveability and prevention of white smoke this approach appears feasible. Some areas requiring further research are outlined.