A number of Australian coking coals were blended and their behaviour during carbonization was examined using proton magnetic resonance thermal analysis (PMRTA) to measure the degree to which the fusion behaviour of blends was affected by interactions between the component coals. Most blends examined showed evidence of interactions. Both significant positive and negative interactions (degree of fusion of the blend respectively greater and less than expected if the coals had acted independently) were observed. When interactions occurred between two coals, the temperature at which the interaction was greatest was independent of the proportion of the coal components in the blend, but the magnitude of the interaction was found to be proportional to x(1-x), where x is the proportion of one component in the blend. The interaction between coals is suggested to be mediated by interchange of volatile material.