This study is concerned with the economic theory of exhaustible resources. My interest in exhaustible resources dates back several years when prof. dr. J. Cramer and prof. dr. C. von Weizsacker stimu­ lated me to direct my research, at the Faculty of Actuarial Science and Econometrics of the University of Amsterdam, to the exploitation of Dutch natural gas. This issue raised many theoretical problems, in which I got gradually more and more involved. I was lucky to find in prof. dr. H. Weddepohl a person prepared to listen patiently and to read and critisize my numerous attempts to solve these problems. The actual work on the present monograph started in 1982 at the Faculty of Philosophy and Social Sciences of the Eindhoven University of Technology, in the context of the program "Equilibrium and Dis­ equilibrium" of the "voorwaardelijke financiering" (universitary financing system). I wish to thank here my supervisors prof. dr. P. Ruys and prof. dr. H. Weddepohl for their comments on earlier drafts of this monograph. When looking back, I realize that their remarks and our dis­ cussions have led to notable improvements. Also the Internation~l Institute for Applied Systems Analysis (Laxenburg, Austria) has made a valuable contribution by offering me the opportunity to spend three months in its serene academic environment in the summer of 1983. Thanks also to the energy group of I. I. A. S. A. and the I. I. A. S. A. foundation Netherlands.