A round robin study to measure the aromatic levels in diesel fuels was conducted by the Chemical Characterization Panel of the Coordinating Research Council Air Pollution Research. Advisory Committee (CRC-APRAC) In-house Program Group, CAPI-1-64. The fuels for this study consisted of a jet fuel, a No. 2 diesel reference fuel, and three fuels used in a CRC-sponsored diesel emission project (CAPE-32) These fuels had 90% distillation temperatures which ranged from 472° to 642° F and aromaticity levels from approximately 18 to 55% by volume.All participants used the American Society for Testing and Materials (ASTM) D1319 or modified D1319 methods to measure the aromatic levels in the selected fuels. Some participants concurrently analyzed the same fuels using other methods such as high-performance liquid chromatography, mass spectrometry, nuclear magnetic resonance spectrometry, and elution chromatography (ASTM D2549). One nonparticipating laboratory analyzed the fuels using supercritical fluid chromatography.The results of nine participants using the D1319 methodology and other methods showed good agreement for fuels with 90% distillation temperatures less than 600° F. However, this round robin study showed that: 1) there is no standard method to measure aromatic levels in full boiling range diesel fuels, and 2) there are inadequacies when using the D1319 and modified D1319 methods for fuels outside of the specified property ranges.