The effect of temperature on four sorbitan ester (Span 20, sorbitan monolaurate; Span 40, sorbitan monopalmitate; Span 60, sorbitan monostearate; and Span 80, sorbitan monooleate) monolayers was analyzed. The covered temperature range was from 22 to 42 degrees C. Surface pressure-molecular area isotherms were measured with a Langmuir-type instrument. As the temperature was increased, the monolayers expanded more. This change can also be seen from the surface compressional modulus that was lowered as the temperature was increased. Also, the collapse pressure was lowered as the temperature was increased. Copyright 2001 Academic Press.