Sufficient conditions applied to an optimal control problem of resource management

The purpose of this paper is twofold. First, by solving an interesting problem in the theory of exhaustible resources, it is exemplified how direct sufficiency conditions should properly be used in optimal control problems. The motivation for this aspect of the paper is the almost complete negligence in the economic literature of dealing properly with sufficiency conditions. Second, an important point in the discussion of J. Aarrestad (Scand. J. Econom., 81 (1979), 522–565) is supplemented.