This paper describes an assessment of char classification system by the Combustion Working Group in Commission III of the International Committee for Coal and Organic Petrology (ICCP). The work of the group culminated in the production of a char atlas after a final round robin exercise. This round robin involved 21 analysts and was an electronic exercise using digitally captured images of individual char particles, rather than actual char blocks. A software program featuring 170 char images was specifically designed to allow operators to identify each char based on a classification system with 9 individual char types; tenuisphere, crassisphere, tenuinetwork, crassinetwork, mixed porous, mixed dense, fusinoid, solid and mineroid. The program electronically recorded all decisions as well as the time taken for each decision to be made. From 170 chars, 128 chars were identified by a majority (>70%) and these chars were then compiled in a char atlas that is now available for download (www.nottingham.ac.uk/-eczehl/charatlas). As would be expected all analysts appeared to become more confident in identifying chars during the exercise, taking less time per image, but with no clear evidence of improvement. Without exception, analysts took longer to make an incorrect decision. (C) 2009 ICCP. Published by Elsevier B.V. All rights reserved.