Fixed order quantity is a method that places a replenishment order when the quantity on hand falls below a predetermined level, called the reorder point. The reorder point is calculated based on the expected demand during the lead time and the safety stock. The order quantity is fixed and constant, and it is determined by the economic order quantity (EOQ)formula or other criteria. Fixed order quantity is also known as the order point/order quantity (OP/OQ) system or the continuous review system.

Option A is not correct, because min-max system is a method that places a replenishment order when the quantity on hand falls below a minimum level, called the order point. The order quantity is variable and depends on the difference between the maximum level and the current inventory level. Min-max system is also known as the two-bin system or the bin system.

Option C is not correct, because periodic review is a method that places a replenishment order at fixed intervals of time, regardless of the quantity on hand. The order quantity is variable and depends on the difference between the target inventory level and the current inventory level. Periodic review is also known as the fixed order interval (FOI) system or the periodic order quantity (POQ) system.

Option D is not correct, because available-to-promise (ATP) is not a method of inventory replenishment, but a calculation of the uncommitted portion of the current inventory and planned production. ATP is used to promise delivery dates to customers based on the availability of inventory and production capacity.

References:

Inventory Management and Control

Inventory Replenishment Methods

Inventory Replenishment Policies