The cationic surfactant dodecyltrimethylammonium bromide (DTAB) was shown to aggregate into micelles in the ionic liquids (ILs), ethylammonium nitrate (EAN) and propylammonium nitrate (PAN) at much higher concentrations than in water. Their critical micelle concentrations (cmc) in EAN/water mixtures first decrease, and then increase with increasing ionic liquid content. Cmcs obtained from titration calorimetry (iTC), conductivity, pyrene fluorescence probing and small-angle x-ray scattering are found to be similar over their respective solvent composition ranges, and the suitability of each technique will be compared. Conductivity was used to measure the cmcs at low IL content in water, and showed that the ionic liquid behaves like a simple electrolyte at low concentrations, but at co-surfactants at higher IL concentrations. Conductivity is not applicable in IL-rich mixtures where the cmc is significantly higher, due to the solvent conductance. Here iTC results are compromised by the decreasing enthalpy of micellization (ΔHm°) which is near zero in pure EAN.