Objects are concurrently manipulated through method issued by multiple transactions in object-based systems. Objects are locked in modes of the methods. Lock modes are defined based on the conflicting relation of method. We define a partially ordered relation on lock modes showing which modes are stronger than others. We newly propose a moderate locking (ML) protocol where an object is initially locked in a weaker mode than a mode intrinsic to the method and the lock mode is finally escalated to the method mode. The weaker the initial mode is, the higher concurrency is obtained but the more frequently deadlocks occur. The ML protocol is evaluated in terms of throughput and number of deadlocked transactions compared with the pessimistic and optimistic protocols.