In this paper we re-examine the problem of optimal forest fire suppression which was previously studied by Parks. The growth of the fire is modelled by a deterministic differential equation in which the level of the suppression forces appears as a control variable. After defining a suitable objective functional to represent the total cost of suppression forces used and the losses resulting from fire damages, we obtain an optimal control problem where the final time is unknown. Using results from control theory we find the optimal level of suppression forces as a nonconstant function of time. © Society of American Foresters, Bethesda, MD. Abstract reproduced by permission.