An experimental and theoretical investigation of the performance of a ballistic compressor is described. Comparison of the computed ideal behavior of the ballistic compressor with experimental test pressures show that the ideal theory overestimates the generated pressure by as much as 30%. An assessment of the factors responsible for the nonideal behavior of the ballistic compressor is given. These factors include: valve losses, external and internal (blow-by) leakage, friction of the inertia! piston, nonideal behavior of the driver and test gases, shock wave formations, and heat losses. The valve losses and both the internal and external leakages have been measured experimentally. A parametric study shows that the choice of equation of state of the test gas is not very critical. The heat loss experienced by the test gas was estimated to be l°7o of the total energy imparted to the test gas. Shock-wave formations have negligible effect on the performance of the ballistic compressor for the mass of the inertial piston (1.34 kg) used.