Abstract: Leakage in buried pipelines poses a major threat to urban infrastructure. Acoustic-wave-based leak localization method is widely used, but its accuracy relies heavily on the precise velocity estimation. Many approaches simplify the soil as a single-phase homogeneous medium. However, high groundwater level and fluid leakage may lead to soil saturation, whose effects on wave velocities require accurate assessment. This study develops a calculation model for the fluid-dominated wave (s=1 mode) velocity by incorporating Biot’s poroelastic theory to represent saturated soil behavior. Steel and ductile iron water pipelines, as well as steel and polyethylene (PE) gas pipelines, are examined to systematically evaluate wave velocity variations with respect to soil type, pipe material, pipe diameter, and internal fluid. Sensitivity analysis is conducted to assess the influence of key soil parameters on wave velocity. The results indicate that for water pipelines with diameters up to DN500 and for all gas pipelines considered, the influence of saturated soil is negligible. In contrast, for DN1000 water pipelines, the velocity difference between saturated and homogeneous soil conditions increases with frequency, reaching a maximum relative error of 18.67%. Porosity, soil bulk modulus and Poisson’s ratio are identified as the key factors. These findings clarify the role of saturated soil in s=1 wave propagation and provide a theoretical basis for accurate velocity determination in pipeline leak localization.