A method is provided for adjusting a fuel composition estimate. The method generally uses a non-fuel related property to determine fuel composition. In some cases the method can be used after refueling and when the engine is operating without the benefit of oxygen sensor data, which can include evaluating data not based on characteristics of the fuel or exhaust from its combustion, such as engine torque variations while using the fuel. The method can include monitoring estimated engine torque to determine whether first variations in engine torque exceed a threshold, and, if so, modifying the previous estimate of fuel composition prior to the refueling event by a pre-determined amount.