The Deepwater Horizon accident in the Gulf of Mexico (2010) focused attention on the unique challenges associated with underwater blowouts in the deep ocean. Plumes of oil droplets generated from deep-water blowouts rise through various layers of the ocean with different dominant physical processes (e.g. stratification, Langmuir turbulence, Ekman transport, surface gravity waves, and submeso-/meso-scale eddies). The interplay between all these processes as well as droplet properties must be considered in predictions of oil spill evolution and in assessments of oil-dispersant application. In this work, the transport of oil plumes in the ocean is studied using large eddy simulation (LES). To accurately represent complex physical processes acting on many different length scales, a multi-scale approach called ENDLESS is developed. ENDLESS is then applied to the conditions of the Deepwater Horizon oil spill, allowing simulation of large horizontal plumes (~20km) with grid resolution of a few meters. For the conditions used in this study, simulation results show that surface application of the dispersant has significant effects on the oil transport – the mean advection velocity of the oil plume is reduced by a factor of 4 and the horizontal diffusivity is increased by a factor of 10 after about 40 h. These effects of surface application of dispersant on oil transport should be considered in the remediation planning of future spills.