The partners of this project have produced two types of important results. First of all, a large set of experimental data has been measured and their accuracy evaluated. These data are relative to: - 6 pure hydrocarbons (C1, C2, C3, C4, C5 and C10). - 8 binary mixtures. - 2 ternary mixtures. - 3 multi-component synthetic mixtures. - 7 real reservoir condensate gases. Next a new semi-empirical viscosity model based on the friction theory has been proposed. This model has further been evaluated with a range of "conventional" North Sea crudes for which viscosity data were available at reservoir conditions. The average absolute deviation of viscosity predictions is around 15%. In contrast, the Lohrenz-Bray-Clark correlation, which is normally used in reservoir simulators, clearly fails to provide any reasonable viscosity prediction for North Sea crude oils. Finally, the viscosity of the real reservoir condensate gases experimentally studied in this project has been computed with this friction theory based model and compared to the measured data. It has been found that the obtained average absolute deviations between 1 and 5% are in agreement with the order of magnitude of the experimental uncertainty (+/-1%). Therefore this project results are satisfactory for most applications related to the oil and gas industry. Considering the economical impact of these results, a reservoir performance as measured in terms of the cumulative hydrocarbons production is sensitive to the viscosity of the fluid stream. For light streams such as the ones which are the target of this project (having a viscosity lower than 0.5mPa.s), simulation work indicates that a +/-10% error on computed viscosity will produce an uncertainty of +/-1-2% on the cumulative hydrocarbons production. In terms of the present oil and gas value, this would correspond to a variation of +/-75 million Euros on the revenue resulting from the reservoir exploitation. This clearly shows that the improvement brought by the results of this EVIDENT project can be extremely beneficial for the economics of reservoirs exploitation within the European Community.