Evaporation is one of the most important processes during an oil spill and needs to be included into the oil spill models. The oil-spill models mostly employ either the Mackay or the Fingas method for description and simulations of evaporation. The Mackay method is a boundary-layer regulated method based on observations of water evaporation. The Fingas approach is not regulated with the boundary layer. NAFTA3d is a 3D Lagrangean numerical model for oil-spill simulations, developed at the UL FGG, The NAFTA3d model was upgraded by adjusting the Mackay method, which is now capable to calculate the evaporation solely from the API-index instead of using numerous input parameters. The model was upgraded by including the Fingas method, which is based on laboratory experiments. In this method the evaporation of oil is described by empirical equations, which are function of temperature and time. Both methods have been intercompared on the same set of input data. We simulated an oil spill in the Gulf of Trieste using two different types of oil: the Brent Blend crude and Prudhoe Bay crude. The simulation results showed significantly higher evaporation using the Mackay method, which affects the other process in the case of an oil spill.