Hypothesis: Mixed solutions of cationic and anionic surfactants show considerable synergism in their wetting behaviour, but their spreading is affected considerably by the phase separation processes. The valuable information about wetting properties of synergetic mixtures can be obtained by using mixtures in which phase separation occurs at concentrations above cmc. Experiments: Spreading properties of mixed solutions of cationic and anionic surfactants over highly hydrophobic substrate such as polyethylene are investigated and compared with those for trisiloxane superspreader. Experiments are performed at relative humidity of 40% and 80%. Interfacial tension at water/air and water/alkane interfaces is measured to explain spreading performance. Findings: Catanionic solutions can wet hydrophobic substrates nearly as effective as solutions of trisiloxane superspreader. The spreading factor reaches 70% of that of superspreader for the most effective mixed solution. The spreading slows down earlier at high surfactant concentrations. At room humidity (40%) spread area has a maximum vs concentration. However, the maximum was not observed at higher humidity 80%. Humidity does not affect the short-time spreading rate, but it influences considerably the time when spreading slows down. The spreading rate of mixed solutions is smaller than that of superspreader despite the same spreading exponent alpha = 0.5. (C) 2015 Elsevier Inc. All rights reserved.