This paper presents an efficient resource sharing scheme for a network supporting multiple service level agreements (SLAs). Specifically, an overloaded SLA can borrow bandwidth from those underloaded SLAs based on a call level service differentiation concept. While flows admitted with the SLA nominal capacity are considered as in profile flows, flows admitted with borrowed bandwidth are tagged as out profile flows and may be preempted later when the original bandwidth owner needs to claim back the resources. Such preemption is considered as the quality of service (QoS) differentiation between the in profile and out profile flows. Through the implementation design and computer simulations, we show that high resource utilization and SLA compliance can be simultaneously achieved by bandwidth borrowing and call level differentiation.