In this paper we estimate two models for interfuel substitution between electricity, district heating and (other) fuels using a micro panel data set containing information for most Danish industrial companies in the period between 1983 and 1997. The main finding of the study is that interfuel substitution is low within the companies, especially between electricity and other fuels. The partial own price elasticities estimated are small (between -0.04 and -0.13) both for electricity and other fuels, while it is between -0.44 and -0.50 for district heating. The partial own price elasticity for electricity is smaller than generally found in macro studies. One explanation may be that the macro studies, in addition to technical substitution, capture some derived demand effect (i.e., aggregation bias).