As a test for postulated influences of sulfur emissions on nucleation, the contrail formation from a two-engine jet aircraft was investigated using fuels with different sulfur contents for the two engines during the same flight. The sulfur mass fractions in the fuels were about 2 and 250 ppm, respectively, typical for aviation fuels. Other engine and fuel parameters were about the same for both engines. Contrail formation was observed visually from distances as close as 100 m and documented by video and photos. The flight took place at 302 hPa (9 km altitude), at ambient temperatures of about -50 ¿C, and relative humidity for liquid water of about 34%. Short contrails formed about 30 m after the engines. No visible differences were detected in the contrails forming from the two engines. The observed conditions for contrail formation are close to those predicted by Appleman [1953> if the propulsion efficiency of the aircraft/engine combination during flight is taken into account. ¿ American Geophysical Union 1995