Condor and Stuart oil shales were pyrolysed with superheated steam at 45G6OOC in a 48 mm diameter semi-continuous fluidized-bed reactor. Temperature had a significant influence on the yields of products and on the ratio of light oils (C, -340ยฐC) to heavy oils (+34o"C). By contrast, the organic carbon conversions to char in spent shale were constant, and the elemental composition of oils changed only slightly over the whole temperature range. The yields of C,-C, alkanes increased linearly with temperature. The relationships between temperature and the yields of other gases (C2-C, alkenes, hydrogen and carbon oxides) were also linear, but with a transition from a low rate of increase to a much higher rate above a certain temperature. This transition temperature was 525ยฐC for Stuart and 550ยฐC for Condor oil shale. Oil yields, which appeared to be constant in the low temperature range, decreased rapidly above the transition temperature. Compared with experiments using nitrogen as the sweep gas, steam pyrolysis produced higher oil yields in the low temperature range. However, above the transition temperature steam was partly responsible for increases in hydrogen and carbon dioxide production at the expense of oil. This would appear to result from steam gasification of kerogen/bitumen/oil vapour catalysed by shale minerals. Low oil vanour concentration in the retort was also found to be essential to reduce oil coking losses within shale particles.