When gas is released in deepwater, the high pressure and low temperature can convert the gases into hydrates, which are buoyant. As these hydrates travel upwards they will encounter regions of lower pressure and can decompose into free gas. The presence or absence of hydrates has a significant impact on the behaviour of the jet/plume due to the alteration of the buoyancy. The free gas may dissolve in water. This paper describes a computer model developed to simulate the behaviour of oil and gas released from deepwater locations in the ocean. The model integrates the hydrodynamics and thermodynamics of the jet/plume with kinetics and thermodynamics of hydrate formation/decomposition. Model formulation and comparison of results with laboratory data for hydrates is presented. Scenario simulations show the behaviour of oil/gas under different deepwater conditions.