Most mathematical models available today to simulate the behaviour and trajectory of oil spills on the water use the Mackay et al [5] formulation that predicts the time evolution of the oil surface area. The accurate calculation of the area that occupy the oil slick is of fundamental importance, since it determines the evaporation, and other important phenomena that affect oil properties changes and the spill impact on the environment. This work presents a critical analysis of Mackay formulation starting from the original Fay [1] and Hoult [3] theory. It is shown that Mackay constants (Akand Bk) are not universal. Moreover, it is demonstrated that they are not constants but variables depending on the oil and water physical properties and consequently should be evaluated for each particular oil spill. The formulation developed is compared with laboratory experiments for the case of spreading in a quiescent water surface. Results show that the proposed formulation gives more realistic results. This analysis helps to better understand this most important problem and should be of interest of those developing and using models to simulate oil spills.
