A method developed for the attainment of economic objectives in single-tool machining operations is extended to multi-tool machining. The stochastic nature of tool life is taken into account, as well as the uncertainty of available information, by introducing confidence level for tool life among the parameters considered. Time and cost penalties due to sudden tool failure are also taken into account. An example pertaining to a simple machining operation shows that under the conditions selected the minimum cost region falls well over the ninety per cent mark of confidence level for tool life.