Sewage sludge was pyrolyzed at different operating conditions with the aim of producing pyrolysis liquid. In this work, the influence of some operating conditions was studied in relation to some liquid properties such as homogeneity (phase separation), solids content, water content, and high heating value. The operating variables studied were bed temperature (450-650 C), inlet nitrogen rate (0.057-0.090 m s(-1)), and solid feed rate per volumetric unit (0.169-0.338 kg s(-1) m(-3)). Phase separation appeared in the samples obtained at almost all operating conditions studied, and it was different depending on the operating temperature and the sample of sewage sludge. The experimental methodology for analyzing the quantitative properties of the pyrolysis liquid under study was based on experimental design techniques. These liquid properties were influenced in different ways by the three studied operating conditions, but above all by the temperature, the inlet nitrogen rate, and also the sample of sewage sludge. Based on the experimental data, empirical models were built to describe the influence of the operating conditions on the liquid properties. Additionally, using these empirical models, operating conditions (within the intervals under study) that allow a high liquid yield and a liquid product with desirable values of the studied properties to be obtained were predicted theoretically.