Kinetics of the coal-hydrogenation reaction have been studied using three systems: (I) catalyst and solvent (vehicle), (2) vehicle only, and (3) catalyst only; within a temperature range of 390-410Β°C. The orders of reaction and the rate constants were calculated using a modified differential equation with respect to the organic benzene-insolubles. For all the three systems the reaction course can be broadly divided into four steps, of which the first two were significant. The reaction orders varied not only from one step to another but also within each step, though over a small range, with temperature. Taking systems (1) and (2). in particular, the reaction orders can be very broadly approximated to 1 .O for the first step, between 1.5 and 2.0 for the second step, and between 0.5 and 1 .O for the third step. Assuming the applicability of the Arrhenius Law, the calculated activation energies for the first step of the three systems are 182, 332.5 and 345.5 kJ/mol respectively. The difference in the activation energies for step 2 of systems (1) and (2) narrowed down to 70 kJ/mol. The distinct sequential variations of the reaction orders indicate not only the interplay of multiple reactions but also the possible influence of intermediates formed during the reaction. In this context, the measured activation energies have limited significance because of the dissimilar temperature coefficients of these reactions and also of the heterogeneity of the reaction species. The mechanistic interpretation of the variation of reaction order will be discussed in Part 2 of the study.