Studies were conducted to quantitatively evaluate the effects of liquid-engine design and operating parameters on two-phase flow performance losses using an N2O4Alumizine-gel propellant combination. The theoretical analysis was made of two-phase flow performance losses resulting from the existence of aluminum oxide in the nozzle exhaust. Particle samples, collected during each 2K engine test, are being analyzed to determine the representative particle size and distribution data for the analysis. A one-dimensional gas- particle flow analysis is being used to determine the performance losses. Preliminary computations indicate that the use of the mass median for particle size classification yields performance losses comparable to those derived when the particle distribution is used in the analysis. Forty-two 2K engine tests were successfully conducted. Some of these tests were performed to resolve the feed system pressure-oscillation and hardware erosion problems encountered in early experimental testing. Observed specific impulse efficiency was nominally 87. Two-phase flow performance losses were calculated to be nominally 2 of the theoretical specific impulse and further, the influence of design and operating variables on two-phase flow performance were found to be in significant at the sea level expansion ratio. The single most significant loss was determined to be energy release loss the absolute magnitude varying with engine design, but was found to be insensitive to mixture ratio or chamber pressure.