This study examines heterogeneity in nonindustrial private forest owners’ timber supply by using a large panel data set of Norwegian landowners. The full sample is divided into more homogenous subsamples. We apply four econometric panel data specifications. Three of the specifications have seldom or never been applied previously in such a supply analysis. Interpretations and results for estimated slope parameters vary substantially between estimators. Supply responses differ considerably with respect to property size and across regions. Changes in roundwood prices and interest rates are the main determinants explaining the decrease in supply during the period 1989–1997. Future roundwood supply analysis should preferably account for heterogeneity in order to avoid inconsistent estimators that could mislead decision makers.