Low-temperature conductivity mechanisms were identified in acceptor-doped SrTiO3 single crystals quenched from high temperatures under reducing conditions. Impedance spectroscopy measurements made on samples of the prototypical perovskite structure doped with iron provided a framework for creating a complete conductivity model for a well-defined point defect system. The dominant conductivity mechanism in the room-temperature range was identified as being controlled by oxygen vacancy hopping. The activation energy for oxygen vacancy migration, an often debated value in the perovskite community, is determined to lie within the range of 0.59-0.78 eV for the iron-doped system with the bottom of this range approaching the intrinsic value for oxygen vacancy hopping in an undoped single crystal. At low temperatures, oxygen vacancies form defect complexes with iron impurities, and the observed range of activation energies is explained and modeled in terms of an oxygen vacancy trapping mechanism.