The aim of this study was to obtain a better understanding of the size exclusion mechanism of coal and petroleum-derived materials in size exclusion chromatography (SEC). To this end a relatively straight forward method was devised and is presented. Results obtained from laser desorption - mass spectrometry (LD-MS) analysis of SEC elution-fractions provide a method for generating an SEC correlation with LD-MS which can accommodate both the retained and excluded regions of the chromatogram. The results suggest that an upper limit of the LD-MS may have been reached when the conditions used in this investigation are employed. Using LD-MS to provide the mass estimations has confirmed, by independent means, that the earlier eluting material from SEC has a higher average mass than the material eluting at longer times.