A new quadrilayer surface phase, and its transition to bilayer and liquid surface phases, are observed by x-ray and surface tension measurements in the surface-frozen layer of a binary mixture of similar to20%C26OH:80%C18OH alcohols. The surface phase diagram is rationalized qualitatively based on the free energy landscape. A quantitative elucidation of the molecular-level origin of these effects is not currently available. (C) 2003 American Institute of Physics.