Slug flow in the air- water system near atmospheric pressure was studied in a 1/2 in. diam tube. Measurements of flow characteristics, pressure gradient, pressure fluctuations, slug velocity and frequency were made for horizontal and inclined Flow. A semiempirical theory based on a simple model was developed. Pressure losses calculated from this theory require a priori knowledge of the slugging frequency. A comparison of the prediction of the theory and two published correlations shows that the proposed theory gives better agreement with the data. 1