Based on experimental shock data of Al'tschuler, Anderson, and Kormer, an equation of state from Zel'dovich is used to estimate thermodynamic characteristics of a porous aluminum target, after impact by iron or aluminum projectiles, in the impact velocity range ∼8–20 km s−1, which produces shock pressures in the range 0.4–8Mbar. The initial target distention,m=&rgr;0/&rgr;00, is varied from 1 to 3. It is found that projectile and target pressures and the projectile thermal energy are monotonically decreasing functions ofm. The thermal energyE′retained in the relaxed target is a monotonically increasing function ofm. The electronic fraction of thermal pressure ranges from a few percent for a nonporous target at 8 km s−1up to 20% at 20 km s−1andm=3. Within the ranges of target density, &rgr;0i, and target distention,m, considered in this study, and in the impact velocity rangeVi=8–16 km s−1, the relative effectiveness of these parameters in producing target heatE′(erg/g) can be roughly characterized by the relationE′∝∼&rgr;0i0.47 m1.49 Vi2.13. The minimum velocity that will produce significant target vaporization in aluminum‐aluminum impact decreases from 18.4 to 7.9 km s−1asmis changed from 1 to 3, whereas that for iron‐aluminum impact drops from 14.0 to 7.4 km s−1.