In this work a new model for tracer diffusivities (D-12) of real systems is proposed. It is applicable for gases, liquids and supercritical fluids over wide ranges of temperature and density. It was derived on the basis of a very accurate hard sphere expression, following a systematic derivation whereby the softness of repulsive interactions and the contribution of attractive forces were taken into account by means of effective diameters and by coupling an attractive exponential term. The model is explicit and requires only temperature, density, and one diffusive parameter. The validation was accomplished with the largest database ever compiled - 314 binary systems and 5421 data points - giving rise to an average deviation of only 4.40%. Finally it must be emphasized the reliable estimation capability of the new model, i.e. its capacity to predict D-12 at temperatures and densities far away from the conditions of the experimental data utilized to fit its parameter. (C) 2010 Elsevier B.V. All rights reserved.