The capability of published two-phase flow equation sets to predict transient propagation behavior has been studied numerically. The equation sets are those cited by Wallis for separated flow and extensions of those used by Rudinger and Chang for dispersed flow. The primary difference between these two sets is that in the set cited by Wallis, the pressure gradient appearing in each momentum equation is weighted by the phase volume fraction, whereas in the extended Rudinger--Chang set, the pressure gradient appears only in the ''continuous'' phase. The original Rudinger--Chang set had to be modified because it can adequately describe only the transient flow of very dilute suspensions of solids in air. This numerical study shows that pressure pulses propagate at essentially the sound speeds obtained from characteristics analysis for the equation sets investigated. Comparisons of numerical results with experimental air-water pressure propagation data show that only the modified Rudinger--Chang equation set exhibits propagation behavior in good agreement with the experimental observations at low (less than 10 percent) void fractions. None of the equation sets adequately predict the experimental pressure propagation rates in the range of void fractions from 10 to 60 percent where the flow regime was observed to change from bubbly to full slug flow. The modified Rudinger-- Chang set explains an apparent discontinuity in the experimental pressure wave propagation speed at a void fraction of 50 percent if the entire pressure gradient is assumed to be carried by the liquid for less than 50 percent voids and by the vapor for greater than 50 percent voids; however, the magnitude of the calculated discontinuity is greater than the experimental discontinuity. (auth).