The analysis of experimental data of flow resistance for two-phase water-tar oil and water-machine oil mixtures is presented in the paper. The investigation has been carried out in hydraulically smooth glass horizontal pipes having diameters of 12, 16 and 22 mm. On the basis of the results obtained from the experiments, the analysis of changes in flow resistance depending on flow rates and fractions of the phases has been made. An effect of two-phase flow patterns on flow resistance has been discussed. A new method for flow resistance calculation has been proposed.