Abstract: The oil-gas multiphase pipelines are widely used in the surface gathering and transportation systems of the oil & gas fields. The pressure drop calculation of the oil-gas multiphase pipeline has significant impact on the economic pipe size determination. Based on four formulae of the pressure drop calculation, including DuklerⅠ, DuklerⅡ, Beggs-Brill (B-B) and Baker, a calculating software is programmed with C++Builder 6.0. The calculated pressure drop of the software is compared with the simulation results of the multiphase simulation software OLGA, and the applicability of different formulae is obtained. Moreover, major influential factors on pressure drop of the oil-gas multiphase pipeline are studied with proper formulae for high-viscosity and low-viscosity crude oil. The pressure variation at different gas/oil ratios, pipeline diameters and flow patterns are obtained.