Structure/function relations in transition metal sulfide catalysts (R.R. Chianelli, M. Daage). Stacking of molybdenum disulfide layers in hydrotreating catalysts (R.C. Ryan et al.). Chevrel phase HDS catalysts: structural and compositional relationships to catalytic activity (G.L. Schrader, M.E. Ekman). Influence of the support and the sulphidation temperature on the catalytic properties of molybdenum sulphide in pyridine hydrogenation and piperidine hydrodenitrogenation (J.L. Portefaix et al.). The effect of phosphate on the hydrodenitrogenation activity and selectivity of alumina-supported sulfided Mo, Ni and Ni-Mo catalysts (S. Eijsbouts et al.). Influence of preparation on the morphology and microstructure of cobalt-molybdenum sulphides (G. Díaz et al.). Effect of 2,6-diethylaniline and hydrogen sulphide on hydrodenitrogenation of quinoline over a sulphided NiO-MoO3/Al2O3 catalyst (C. Moreau et al.). Search for simple model coupounds to stimulate the inhibition of hydrodenitrogenation reactions by asphaltenes (C. Moreau et al.). The versatile role of nickel in Ni-MoS2/Al2O3 hydrotreating catalysts as shown by the use of probe molecules (J.P. Bonnelle et al.). A history of the development of high-metals hydrotreating catalysts. The use of crystallographic concepts in catalyst design (H.D. Simpson). Structure of bimetallic catalysts Pt/Sn on SiO2 vs. Al2O3 supports: NEXAFS and EXAFS diagnostics (N-S. Chiu et al.). Mössbauer study of the sulfidation of hydrodesulfurization catalysts: so-called ``Co-Mo-S'' phase observed in carbon-supported Co and Co-Mo sulfide catalysts (M.W.J. Craje et al.). A new approach for studying the acid strength distribution in hydrotreating catalysts by differential scanning colorimetry (A.K. Aboul-Gheit, A.M. Summan). Supported Co-Mo thin film sulphide catalysts for hydrodesulphurization. 1. XPS studies of the effects of reactant pressure (N.S. McIntyre et al.). Adsorption, reaction and desorption rate constants in heterogeneous catalysis, measured simultaneously by gas chromatography (N.A. Katsanos, J. Kapolos). A miniature on-line closed-cycle reactor for X-ray photoelectron spectroscopy studies of hydrodesulphurization reactions (P.A. Spevack et al.). Catalytic properties in hydrotreating reactions of ruthenium sulphides on Y zeolites: influence of the support acidity (S. Gobolos et al.). Upgrading of coprocessed naphtha by hydrotreating (M.V.C. Sekhar, P.M. Rahimi). Improved hydrocracking performance by combining conventional hydrotreating and zeolitic catalysts in stacked bed reactors (A.A. Esener, I.E. Maxwell). The microbial upgrading of model heavy oils (L.E. Patras, I.A. Webster). Author Index. Subject Index.