Simple inventory models are developed for fast moving spare parts subject to the risk of unexpected, immediate obsolescence. The approach does not require a precise knowledge of the probability distribution of the moment of obsolescence, as is the case for models discussed in the literature. A rough estimate of the obsolescence risk for the next order cycle is sufficient.The models can be seen as extensions of the EOQ-formula. Following cases are studied:1. Constant obsolescence risk; no shortages allowed2. Varying obsolescence risk; no shortages allowed3. Varying obsolescence risk; shortages allowedIt appears that the models are practicable and, in the proper circumstances, lead to a substantial reduction of cost.