A set of low-sulfur diesel fuels from the Western Pacific region were found to be unstable during storage although they passed all standard specification tests. This sample set was found to have high nitrogen content. Initially, liquid liquid extractions with a mild aqueous acid were performed to separate basic and nonbasic nitrogen groups in an attempt to determine if these organonitrogen classes were responsible for the poor stability. The findings of this study indicate that there may be a correlation between the acid-extractable nitrogen compounds in these fuels and the formation of high levels of particulates in storage. To develop a more comprehensive understanding of the classes and distributions of organonitrogen compounds in fuels, a novel analytical method was developed using two-dimensional gas chromatography with nitrogen chemiluminescence detection (GCxGC-NCD). The GCxGC-NCD analyses revealed the presence of three distinct groups of nitrogen compounds. One group corresponded to the acid-extractable basic nitrogen compounds, one with the nonbasic nitrogen compounds, and a third early-eluting lighter polar organonitrogen fraction that had previously not been observed. This light organonitrogen fraction was unique to these particularly unstable fuels. If this is found to be universally applicable, this light polar nitrogen fraction may serve as an indicator of potentially unstable diesel fuels. Overall, the GCxGC-NCD method has been shown to be a valuable tool to enhance our understanding of the chemistry of organonitrogen species and their impact on fuel stability.