The mode of occurrence of trace elements in coal is important from both scientific and environmental viewpoints because the behavior of trace elements in coal utilization depends not only on their concentration but also on their chemical form or mode of occurrence. Statistical methods are one of the more commonly used indirect approaches for interpreting element modes of occurrence. These methods include correlation coefficients between elements and ash as well among the elements themselves, cluster and factor analysis. Using data sets derived from a suite of 75 samples from a Bulgarian lignite deposit we demonstrate that statistical analysis of subsets with different ash ranges and with slightly different suites of elements can lead to substantially different conclusions concerning the element modes of occurrence. In this example we assume that direct information on the element modes of occurrence, such as mineralogy or selective leaching behavior, is absent. Statistical methods, however, can provide useful insights into trace element modes of occurrence for properly constrained sample suites. (C) 2010 Elsevier B.V. All rights reserved.