Processing parameters to minimize the residual oxygen content of ZrB2 ceramics prepared by reactive hot-pressing were selected using statistical analysis. Additions of carbon and excess boron were used to react with oxygen present in the starting ZrH2 and B powders as an impurity. A 32 full-factorial experimental design was used to determine the carbon and excess boron contents that minimized residual oxygen content in the final ZrB2 ceramic while also minimizing formation of any impurity phases. Carbon additions were effective at reducing the oxygen content, but resulted in the formation of residual ZrC. Boron additions were also effective at removing oxygen, but to a lesser extent compared to carbon. In addition to being more effective at removing oxygen, carbon additions also improved the densification behavior, whereas boron additions inhibited densification. The stoichiometric reaction resulted in a ZrB2 ceramic with a relative density of 99%, but that contained 6.9 vol% of (Zr1-x,Mgx)O2-x as a residual phase following reactive hot-pressing. The composition with a carbon addition to starting oxygen content having a molar ratio of 1, and a boron to zirconium molar ratio of 2.1, resulted in a 95% dense ceramic with only 0.1 vol% of residual (Zr1-x,Mgx)O2-x and trace amounts of ZrC.