The effect of pipe inclination on upward two-phase slug flow characteristics has been studied both experimentally and theoretically. Experimental data were acquired for the entire range of inclination angles, from horizontal to vertical. New correlations were developed for slug length and liquid holdup in the slug body as a function of inclination angle. A unified model has been developed for the prediction of slug flow behavior in upward inclined pipes. Reasonable agreement is observed between the pressure drop predicted by the model and the experimental data.