The primary barrier to the use of ethanol in diesel fuel is the poor miscibility at lower temperatures. The miscibilities of ethanol in 19 diesel fuels having a wide variation in compositions were evaluated by testing their phase separation temperatures. The result shows that aromatic contents and intermediate distillate temperatures have a significant impact on miscibility limits. The FCC diesels, which contain up to 50% of aromatics, exhibit different phase behavior trends in comparison with straight-run diesels and other diesel fuels. The primary barrier to the use of ethanol in diesel fuel is the poor miscibility at lower temperatures. The miscibilities of ethanol in 19 diesel fuels having a wide variation in compositions were evaluated as testing their phase separation temperatures. distillate temperatures have a significant impact on miscibility limits. The FCC diesels, which contain up to 50% of aromatics, exhibit different phase behavior trends in comparison with straight-run diesels and other diesel fuels.