The catalytic degradation of polyethylene over two commercial cracking catalysts, containing 20% and 40% ultrastable Y zeolite, respectively, was studied in a semi-batch reactor. More specifically, the effect of the polymer to catalyst ratio - expressed as the acidity content of the polymer/catalyst system - was studied on the formation of liquid hydrocarbons. After a sharp increase at small values, the liquid yield seemed to have a negative correlation to the acidity content, showing a maximum at acidity values around 7% of pure US-Y. Regarding the boiling point distribution of the liquid fraction in systems with higher content of active catalyst, a shift was generally observed towards lighter products. Comparing liquid samples during the same experiment, later samples contained heavier components with the exception of the system with the smallest US-Y content of this study. (c) 2005 Elsevier B.V. All rights reserved.