Neogene sequences in the Mahakam delta, Indonesia, contain many coals for which abundant analytical and Rock-Eval data exist. It is essential that raw analytical data are adjusted for the effects of mineral matter, including pyrite, before they are used to calculate atomic H/C and O/C ratios; these ratios are required in order to present the coal series on a van Krevelen diagram. In this paper, a method of adjustment is proposed which allows the definition of a well-constrained Mahakam coal band; this is comparable to the Late Cretaceous and Tertiary New Zealand coal band and the Japanese Palaeogene coal band The relationships between: (i) coal rank (using the Rank(S) scale) and Rock-Eval parameters; and (ii) coal rank and vitrinite reflectance for the Mahakam coals are generally similar to those for the New Zealand coals.