High-sulfur shale oils from two marine oil shales, were subjected to hydropyrolysis using NiMo catalysts deposited on Al-SBA-15 with Si/Al ratios ranging from 10 to 75, i.e. with decreasing acidity, both in a flow-through system at 0.1 MPa H2 pressure and in sealed autoclaves at varying H2 pressure (1–6 MPa (cold, i.e., at room temperature)). For autoclave pyrolysis of El-Lajjun shale oil catalysed by NiMo-Al-SBA-15 (Si:Al = 10:1), sulfur content of oil decreased with H2 pressure, catalyst:oil ratio and temperature, pyrolysis time having little effect. The conditions finally adopted were 400 °C, 6 MPa (cold) H2 pressure, 30 min pyrolysis time and (0.1:1.0) catalyst:oil ratio. Lower Si/Al ratios gave the same hydrodesulphurization (HDS) activity, but coking declined with decreasing Si/Al ratio, so that the optimum ratio was 10. The oil obtained in catalysed pyrolysis contained almost no thiophenes or benzothiophenes