Quantification of the amount of inertinite that is fusible during coke making has long been a goal for many researchers and coke makers alike. This study has used matched halves of coal and coke to first determine the fusibility cut-off, and has then used CSIRO's CGA optical imaging system to obtain quantitative compositional information on individual coal particles at the size they are used for coke making. The reflectance cut-off between fusible and infusible inertinite was determined by cutting coal lumps in half and coking one half. Comparison of matched structures in images of the coal and coke lumps allowed the fusible/infusible reflectance cut-off for inertinite to be determined for each of the coals. This study found that rather than there being a single reflectance cut off point between fusible and infusible inertinite for each coal there is a consistent difference (range) between the end of the vitrinite reflectance distribution and the fusible/infusible inertinite reflectance boundary for each individual particle within a coal. This reflectance range was then used to estimate the amount of fusible and infusible inertinite in individual particles of coal which had been crushed for use as coke oven feed for six Australian coking coals (consisting of matched pairs of coals of similar ranks from different Australian coal measures). Also determined was size detail for the individual inertinite structures within each particle and the amount of infusible inertinite structures greater than 1.5 mm in length. The CGA results obtained suggest that two of the coals (from the Rangal Coal Measures) contained a greater proportion of large infusible inerts than did the coals of comparable rank from other Australian measures. If this is proven, the information may assist coal producers to develop specific milling strategies for these coals. Crown Copyright (C) 2015 Published by Elsevier B.V. All rights reserved.