The overall objective of this paper is to analyse the price development and price formation for wood fuel used by the Swedish district heating sector. According to Lönner et al., there is a significant potential for increasing the use of wood fuel in Sweden, at a fairly moderate cost. The basic question raised in this paper is then why this potential is not realized. Specifically, a methodology is proposed for testing whether the reason is that market imperfections are present. As a first step the shape of the technology in the Swedish district heating sector is estimated for the period 1989 to 1996. In the second step the estimated technology and the assumption of cost-minimizing firms are combined to calculate shadow prices, i.e. marginal valuation of wood fuel in this sector. If the average shadow price significantly deviates from the average observed price one may conclude that this market is functioning inefficiently due to imperfections. According to constructed bootstrap confidence intervals this difference is significant only for three out of eight years, implying that the quantities of wood fuel traded are too small. For the other years the difference is not significant, implying that one cannot, on statistical grounds, reject the efficient market hypothesis for all years.