The purpose of this work is to carry out critical two-phase flow experiment and compare the results with the existing theoretical models to select the most accurate analytical model. For this purpose, an experimental apparatus has been set up and a series of experiments have been carried out for somewhat long pipes (L/D = 108.89 and 51.76). As for the theoretical models, Moody``s model and Henry-Fauske``s model are chosen and tested along with another model which incorporates two existing models. It has been found that the values predicted by these theories are greater than the measured values for long pipes.