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Studies were conducted to quantitatively evaluate the effects of liquid-engine design and operating parameters on two-phase-flow performance losses using an N2O4/Alumizine-gel propellant combination. The theoretical and experimental efforts, conducted concurrently, consist of performance evaluations covering a range of variables sufficiently wide to provide an adequate basis for predicting specific impulse for large-scale engines. The theoretical analysis was made of two-phase-flow performance losses resulting from the presence 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 sea-level and thirteen simulated-altitude 2K engine tests have successfully been conducted. Of the altitude tests, all but two are considered to be valid performance runs capable of providing information concerning the effects of area ratio on two-phase-flow performance losses.