Many high-performance networks support both advance and immediate bandwidth reservations, the former reserving bandwidth ahead of time in a future time slot to provide guaranteed bandwidth, while the latter allocating bandwidth upon availability in the next immediate time slot. As a result, an ongoing data transfer task based on an immediate reservation may be preempted by the activation of an advance reservation due to the lack of bandwidth. We propose a bandwidth reservation solution to optimize network resource utilization by exploring the interactions between advance and immediate reservations. This solution integrates two major interrelated components: (i) We design a scheduling algorithm based on rigorous statistical analysis of reservation dynamics to route incoming advance reservations with minimal impact on immediate reservations. (ii) We design a preemption scheme to minimize the actual number of immediate reservations that must be preempted at runtime due to insufficient bandwidth. The performance superiority of the proposed bandwidth reservation solution is illustrated by extensive simulations in comparison with existing methods.