We present a high-performance decentralized prefetching protocol for the delivery of VBR video on demand (VoD) from servers to clients across a packet-switched network. The protocol gives constant perceptual quality for high link utilizations. It also allows for immediate commencement of the video upon user request and near instantaneous response to viewer interactions such as pause, resume and temporal jumps. The protocol requires that (1) the client has a moderate amount of memory dedicated to the VoD application (2) the client sends a positive acknowledgment back to the server for each received video frame. Our decentralized prefetching protocol employs window flow control. A send window limits the number of frames a server is allowed to send in a frame period. The send window grows larger than one when the network is underutilized, allowing the server to prefetch future frames into the client memory. When the network becomes congested the send window is reduced and the server is throttled. Simulation results based on MPEG encoded traces show that our decentralized prefetching protocol compares favorably with other prefetching protocols in the existing literature.