High-fidelity cyber-physical testbeds that mimic the cyber and physical responses of real-world systems are required to investigate the vulnerabilities of industrial control systems. This chapter describes the construction of a large, virtual, high-fidelity testbed that models a midstream oil terminal. The testbed models interconnected tank farms, a tanker truck gantry, a shipping terminal and a 150 km pipeline connection to a refinery. The virtual midstream oil terminal helps experiment with cyber attacks, explore the impacts of cyber attacks in order to prototype and evaluate security controls, and support education and training efforts. The virtual midstream oil terminal is constructed using a novel modular modeling technique that segments the overall system into the physical system, cyber-physical link, distributed controllers, communications network and human-machine interface. Simulation results involving normal operations and cyber attack scenarios are presented. The midstream oil terminal testbed demonstrates that large-scale models of industrial control systems for cyber security research are feasible and valuable.