Effective inventory management is crucial for optimizing resources and ensuring smooth maintenance operations. This paper explores two primary replenishment systems-Economic Order Quantity (EOQ) and Order Level Control-designed to address the challenges posed by demand variability and lead-time uncertainty. The EOQ model determines the optimal order size to minimize total inventory costs, while replenishment systems guide the timing of orders. We analyze the Fixed Order Quantity System (Q System), which maintains a constant order size with variable ordering frequency, and the Fixed Order Interval System (P System), which fixes the ordering intervals but varies the order size. Each system's advantages and challenges are discussed, highlighting their applicability based on demand stability, lead-time consistency, and inventory value. Through a comparative analysis, this paper provides insights into selecting the appropriate replenishment strategy to achieve efficient inventory control, cost minimization, and resource optimization.