The number of accidents in oil and gas refineries/storage terminals are increasing worldwide. Such events are disastrous to both human beings and infrastructure. It is therefore necessary to utilize the best methods to study worst-case scenarios associated with a process and/or plant. Computational Fluid Dynamics (CFD) models are appropriate to perform 3D modeling of major events with all necessary details. The present work reports the 3D CFD modeling of large-scale flammable cloud dispersion in a real configuration. The most widely approved CFD code for dispersion and explosion simulation FLACS (Flame Acceleration Simulator) is used to simulate the gases released with different flow rates in storage terminals. It was assumed that leak began near the pipes supplying fuel to the storage tank. The flow rate, surrounding condition and release duration were varied to study their influence on overall vapor cloud size i.e. diameter, height and explosive strength. Depending on the extent of LFL and UFL (Lower and Upper Flammability Limit) total flammable volumes of the clouds were predicted. It was found that such detailed modeling helped to understand the dispersion behavior much better than the phenomenological models. The strategic decisions on gas detectors layout can also be made for loss prevention and control. The simulation of worst-case scenario provided guidelines for pre- and post-incident mitigation measures.