In this paper, we discuss the design and use of an object-oriented framework for simulating a two-echelon inventory system. We present how the framework can be used to simulate the backorder and load building queues at the warehouse level of the system. In addition, we describe the modeling options for the backorder processing for replenishment orders sent to the warehouse. Filled orders must then be consolidated into loads for shipping to the retailer level. The framework is built on a Java Simulation Library (JSL) and permits easy modeling and execution of simulation models. A set of experiments is performed to illustrate how queueing disciplines for the backorder and load building queues effect the lead-time experienced at the retailer level. In addition, we summarize future research efforts to model complex supply chains.