The effects of pulping variables on enthalpy of slash pine kraft-black liquors from a 2(k) + 2k + 1 (k = 4) central composite design pulping experiments that were performed in a large pilot scale digester have been studied. The four cooking variables were effective alkali, sulfidity, cooking temperature, and time at temperature. In all cases, the white liquor was adjusted to a causticizing efficiency of 85% and a reduction of 93% with Na2CO3 and Na2SO4. The enthalpy of these liquors was determined over wide ranges of temperature and solids concentrations using a Setaram C-80 calorimeter. In this work, our previous models for enthalpy-concentration relations were used to perform a systematic study on the effects of pulping conditions on enthalpy and to develop statistically based quantitative models for enthalpy as a function of pulping variables. These results are presented, and their utility is discussed.