Pyrolysis of an organic concentrate from municipal solid waste was carried out using a bench-scale fluidized bed reactor at 350-540 degrees C comparing Al2O3 with activated olivine sand as bed materials. A maximum oil yield of 50 wt.% was obtained using the activated olivine sand at 400 degrees C while only 45 wt.% was obtained at 500 degrees C using Al2O3. The bio-oils using activated olivine sand at 400 degrees C had an H/C ratio of 1.50 and O/C ratio of 0.37 and were less aromatic and less nitrogenous compare to the oils obtained using Al2O3 at 400 degrees C where the H/C ratio was 1.32 and the O/C ratio was 0.44. The aromatic compounds were found to be reduced while the aliphatic compounds increased in the oils generated using activated olivine sand. The calorific value of the bio-oil at 500 degrees C was 29 MJ/kg using activated olivine sand while the bio-oil using Al2O3 was 23 MJ/kg. The presence of iron, magnesium and other oxides probably promotes the removal of oxygen, which indicates that the activation energy of C-O bond breakage is reduced compared to the C-C bonds, thus promoting dehydration, decarboxylation and alkalation reactions to produce aliphatic fatty acid at lower temperatures. (C) 2011 Elsevier B.V. All rights reserved.