ABSTRACT:Static 96‐hour median lethal concentrations were determined for the water‐soluble fraction (WSF) of both petroleum‐derived and shale‐derived avaiation fuels (JP‐4 and JP‐8) using fathead minnows. JP‐8 was more toxic than JP‐4 except for one shale JP‐4 sample that was as toxic as the JP‐8. Petroleum and shale JP‐8 were similar in toxicity. The toxicity of shale JP‐4 was less clear. Shale JP‐4 from three vendor sources revealed differing toxicity values. One shale JP‐4 sample was more toxic and one less toxic than its petroleum analogue, with the third being equally toxic. Toxicity of the fuels may be enhanced by compounds in the WSF that correspond to chemicals contain