Mathematical model of fractional distillation of petroleum products (FDPP) has been developed. The model includes four parameters: T-HK -- initial boiling point, T-KK -- end point, a, k - respective coefficients of intensity and symmetry of the FDBP curve referring to mean boiling temperature of the petroleum product. Different methods of determination of FDPP parameters are given based on the properties of the FDPP parameters. These methods can be applied both to full data of the whole curve and incomplete data of FDPP (volume fraction of the distillate smaller than 90%). Some inaccuracies which occur during fractional distillation of petroleum products have been found. The model developed allows us to perform computer analysis of the FD data taking into consideration the mistakes which occur during the process, thus we are able to increase the accuracy and reproducibility of the results.