Victorian brown coal represents a significant resource for power generation in Australia. The typical ash content for these coals can be as low as 1% (dry basis). While low ash content is obviously a major advantage for the utilisation of these coals, it is a problem for researchers in that the low ash content leads to large inaccuracies when using the 'ash tracer' method to determine coal conversion in flow reactors. To address this problem, a modified ash tracer method has been developed to determine coal conversion which involves adding perlite as an artificial ash to the coal. This method has been successfully applied to measure coal conversion during the pyrolysis of Loy Yang coal in a drop tube furnace. (c) 2005 Elsevier Ltd. All rights reserved.