In this paper we consider a single buyer who wants to outsource the manufacturing of a product to N potential suppliers. The buyer’s objective is to maximize the service level she receives from the suppliers. The suppliers compete for the buyer’s demand based on a competition parameter which the buyer announces along with an allocation rule. We model each supplier as a make-to-stock queueing system. Using a simple proportional allocation function, we compare two competition parameters: service level and inventory level. We show that inventory competition creates a higher overall service level for the buyer. We also show an optimal form of competition parameter which can induce the maximum feasible service level. Our base model shows the res...