Investigations with run-of-mine (ROM) coal have been carried out in a small high-pressure fluidized-bed combustor. The coal was 3/4 inch x 0 Pittsburgh No. 8, with a moisture content of 3 1/2%. The objective of the tests was to compare the performance (combustion efficiency, sulphur capture, NO/sub x/ emissions) with that obtained with dry, crushed coal. The coal was fed into the lower part of the fluidized bed using a system of pressurized screws. Apart from being pressurized, these screw feeders were conventional. The final injector screw was about 3 1/2 inches diameter, running at a high, constant (170 rpm) speed; i.e. it was operating substantially empty. The coal feed contained a number of large shale particles. The bed sampling systems indicated that a proportion of these (and also of large coal particles) circulated freely in the bed below the tube bank, and to some extent within the tube bank. There was a gradual segregation process, however, in which the large particles settled on to the distributor. These large particles were mostly removed between the sparges of the distributor, so that defluidization did not occur. If there had not been provision for removing these large particles, the bed would undoubtedly have defluidized within a few hours. Post-test inspection showed no sintering or agglomerations in the bed or on the coal nozzle/injector screw. However, some sintering of coal to form discrete lumps up to 1 1/2 inch in size occurred, possibly influenced by the size and swelling characteristics of the coal. These particles were too large to pass between the sparges. There were insufficient of them to build up to the air nozzle holes and affect fluidization. As expected, combustion efficiency was greater than 99% at a bed temperature of 1560/sup 0/F. Sulphur retention was perhaps slightly lower than with crushed coal at the same conditions, although there were insufficient data to be sure of this point.