The molecular structure of the extractant and diluent strongly affects the critical fluctuations at room temperature, both in magnitude and the location of the Widom line. Figure shows how decreasing diluent chain length reduces the strength of fluctuations. This occurs because the shorter diluents reduce T C , which is consistent with how shorter alkane diluents are widely understood to promote inhibit third phase formation. 44, The fact that trends in third phase formation are consistent with trends in concentration fluctuations of the binary mixture suggests a similar mechanism of extractant/diluent compatibility in both cases. The description of shorter alkane diluents better wetting or solubilizing the metal-extractant complexes/reverse micelles, inhibiting their self-association, is consistent with the reduced concentration fluctuations we observe in simplified binary organic phases.