O Rostro beach was one of the most seriously affected beaches during the Prestige oil spill along the “Costa d'a Morte” in Galicia, Spain, in November 2002. More than 10,000 tons of residual material were removed from the beach, with a significant quantity of the oil buried in the sandy sedimentary column of the beach. Under sporadic wave conditions throughout the years, this situation made the clean-up activities very difficult. Among the reasons why a significant quantity of oil was buried in the beach are the following: first, the arrival of large quantities of oil to the beach; second, an elevated number of high wave energy storms with atypical sequence in direction; and third, the particular morphodynamic features in O Rostro Beach, which is an intermediate bayed beach with a stable middle-scale transversal bar-horn system that, interacting with the local dynamics, has a high capacity to bury oil in sand matrix (2 to 3 m deep). The information collected in the 3-year exhaustive monitoring plan (spring 2003 to summer 2006) in O Rostro Beach has provided better knowledge and comprehension of the processes involved in the interaction of the oil spill dynamics with the beach morphodynamics. Based on these field data, the zones with deeply buried oil were located; also, it was evidenced that 4 years after the oil spill, the buried oil degraded rapidly. A conceptual evolution model of the oil leaked to the beach is proposed, with the aim of explaining how and where the oil initially arrived, where it was buried in the sandy core, and how the oil has evolved physically and mixed with sand throughout the last several years. Based on the conceptual evolution model of the oiled substance, the morphodynamic characterization of the beach, and the field data collected, the clean-up activities have been optimized and significantly improved in O Rostro Beach.