A fluidised-bed combustor has been built to investigate the effect of pressure (up to 20 atm) on combustion efficiency, sulphur retention, NO/sub x/ emission, heat transfer and elutriation. The combustor contained more cooling surface than in Tests 6 and 7 and the main objectives of the test were to obtain data at 20 atm pressure and to operate at lower values of excess air than hitherto. Because of air compressor problems during the test, operation at 20 atm had to be limited to one section. The results, taken together with results from Test 7, indicate that reducing the size of the dolomite feed from 3/32 inch x 0 to 1/16 inch x 0 has not had any significant effect on sulphur retention. Actual values of sulphur retention varied from 93 1/2% at a Ca/S mol ratio of 1.65 to 97% at a Ca/S mol ratio of 2.2. SO/sub 3/ emissions were less than 2ppM except in the final section when, for no obvious reason, measured emissions were in the range 10 to 20 ppm. Combustion efficiency was 99 1/2% or higher at all the conditions. NO/sub x/ emissions varied between 0.22 and 0.36 lb/10/sup 6/ Btu, depending on the excess air. Alkali vapour concentration were measured in the freeboard and at the cyclone outlet. Concentrations were .05 to .15 wppm Na and .05 to 0.2 wppm K. These values are too low for reliable detection of any condensation of alkali between the two measuring points.