In contrast to the long-held belief that only amphiphilic molecules can form stable Langmuir monolayers, we show here that even nonvolatile hydrophobic oils can be reversibly spread into liquid-condensed Langmuir films, if the material is in or close to liquid-crystal phase in the bulk. The stability origin of the hydrophobic Langmuir monolayers is entropic, rather than energetic as in the stabilization of common amphiphilic monolayers, primarily driven by the interaction between the polar head and water. This extraordinary spreading mechanism may have impact on the nature of colloidal and biomembrane stabilities.