Measurements of wave characteristics have been conducted in a 0.0762 m internal diameter (ID) pipe at inclinations of 0 degrees, 10 degrees, 20 degrees, 45 degrees, 60 degrees, 75 degrees, and 90 degrees from horizontal. Wave celerity and frequency are very strongly dependent on modified LockhartMartinelli parameter, X*, and the inclination angle. Wave amplitude increases with increasing liquid film thickness at the bottom of the pipe. Wave amplitude depends on liquid film thickness for any pipe diameter, surface tension, and viscosity. Strouhal number (dimensionless wave frequency) decreases with increasing X*. Effect of pipe diameter, surface tension, and liquid viscosity on the liquid film Reynolds number, ReLF, was studied. ReLF variation with X* is not sensitive to the surface tension and less sensitive to the pipe diameter. However, ReLF is very sensitive to the viscosity of the flowing liquid. Correlations for wave celerity, amplitude, frequency, and liquid film Reynolds number are proposed. (C) 2011 American Institute of Chemical Engineers AIChE J, 2012