Natural olivine was used as bed material during the gasification of plastic waste in a pilot-scale bubbling fluidized bed reactor. The results indicate that it works as an excellent in-situ tar reduction agent, considerably improving the quality of the gas produced, in terms of low tar content, high hydrogen volume fraction and large syngas yield. The phenomena concurring to the activation of the catalyst are described together with those that can contribute to deactivate it. A phenomenological description of the different stages occurring during gasification of plastic waste in a fluidized bed of olivine particles is also reported. (C) 2008 American Institute of Chemical Engineers.