Energy spectrum functions computed from data of various three-dimensional simulations of forced isotropic turbulence are investigated. The piece-wise parabolic method (PPM) was used to treat flows with Mach number of the order unity. The dissipation is of purely numerical origin. For the dimensionless mean rate of dissipation, we find values in agreement with results from other, mostly incompressible turbulence simulations. The so-called bottleneck phenomenon is also present in the turbulence energy spectra. Although the bottleneck reduces the range of nearly inertial scales considerably, we were able to estimate the value of the Kolmogorov constant. In the statistically stationary regime, C ≈ 1.7 for strictly subsonic turbulence, but also in the presence of shocklets in moderately transonic flows. As compressive components become more significant, however, the value of C appears to decrease. Moreover, we discuss length scales related to numerical dissipation, in particular, an effective numerical length scale ∆ eff , which can be regarded as the characteristic smoothing length of the implicit filter associated with the PPM.