p-Xylene, 1008 g, and a (450:630 w/w) p-xylene-Me 4-methylbenzoate mixt. (+ catalyst) were oxidized to dimethyl terephthalate with (i) 20:80 and (ii) 25:75 v/v O-2-N-2 at 0.8 MPa, 150 degrees C, In a reaction calorimeter until the effluent contained 5-6 vol. % O-2. Conversions were (i) 87, (ii) 91 and (i) 80, (ii) 70%, resp.; (reaction + absorption) heats were 42.5-44 and 43.7-44.2 kJ1mol O-2, resp. Thermal powers were (1) 150 and (11)180 W, regardless of reactant type. Stirring (600 to 900 rpm) raised the heat power (69 to 103 W) and reduced 02 at outlet (5.7 to 1.2%). The reaction proceeded In the diffusion (never kinetic) range. With the mixt. as reactant, an Induction period (8-14 min) occurred over which O-2 should be max. 5%. More O-2 as oxidant raised oxidn. rates (by 20%), p-xylene conversion, and heat evolved (by 20%).