Hydrogen gas is produced on a pilot scale by steam gasification of charred lignocellulosic waste material. It is also produced from solid wastes by pyrolysis. In this study, olive husk samples were subjected to direct and catalytic pyrolyses to obtain hydrogen rich gaseous products at desired temperatures. The samples, both untreated and impregnated with catalyst, were pyrolysed at 775, 850, 925, 975 and 1025 K temperatures. The total volume and the yield of gas from both pyrolyses increase with increasing temperature. The largest hydrogen rich gas yield obtained from olive husk, using about 17% ZnCl2 as catalyst at about 1025 K temperature, is 70.6%. In general, in the pyrolysis of biomass, the yield of the hydrogen rich gaseous product increases with ZnCl2 catalyst, but the yield of pyrolytic gas decreases in spite of increasing the yield of charcoal and liquid products. The catalytic effect of K2CO3 was greater than that of Na2CO3 for the olive husk. (C) 2001 Elsevier Science Ltd. All rights reserved.