『(Abstract)
　This paper attempts to reconcile the theoretical predictions of increasing real prices for nonrenewable natural-resource commodities obtained from Hotelling-style models with the empirical findings of falling prices for these commodities. A theoretical model for relative-price movements is derived for the case of exogenous technical change and endogenous change in the grade of ores mined. The model suggests a U-shaped time path for relative prices. The implied price movements are tested for all the major metals and fuels and the model parameters are found to be statistically significant for 11 out of the 12 commodities tested.』

I. Introduction
II. Long-run pricing model
III. Data sources
IV. Empirical results - Quadratic and linear trends
VII. Summary and conclusions
Acknowledgments
References