This study evaluates the effect of ether additives (ETBE and TAEE) in diesel and of ether/ethanol/diesel blends on the properties of density, volatility, viscosity, characteristics at cold temperatures, cetane number and performance in engine tests. The formulations were carried out with 5, 10 and 20% v/v of ethyl ter-butyl ether (ETBE) and ter-amyl ethyl ether (TAEE) and with 5, 10 and 20% v/v of ether/ethanol blends (50/50% v/v) starting from a base diesel. The formulations containing up to 5% v/v of TAEE displayed satisfactory results in the evaluation of physicochemical properties and greater efficiency in the engine tests. The results indicate that the ETBE and TAEE ethers act as cosolvents of ethanol in diesel. The presence of ethanol and ETBE significantly alter the characteristics of volatility (flashpoint and distillation curve) and. reduce the cetane number, impairing the fuel's performance in engine tests. (C) 2005 Elsevier Ltd. All rights reserved.