We use electron paramagnetic resonance (EPR) spectroscopy and photo-induced EPR to discern the compensating species associated with the Fermi level extracted from temperature-dependent Hall measurements of vanadium-doped 4H SiC and high purity semi-insulating 4H SiC. The results demonstrate that the V 4+/V5+ transition is responsible for the 1.6 eV carrier activation energy (Ea) measured in some of the vanadium-doped samples. In other vanadium-doped wafers, photo-EPR data reveal transitions for V3+ at energies between 1.1 and 1.25 eV, consistent with the activation energy. However, the relationship between V3+ and E a is not clear. The carbon vacancy (Vc), which is detected in all HPSI wafers, exhibits a range of photo-thresholds similar to the varying values measured for Ea. Therefore, although EPR measurements show that the number of uncompensated carbon vacancies is below that thought necessary to neutralize the residual shallow donors and acceptors, Vc likely participates in compensation.