Reflection-absorption Fourier transform infrared (RA FT-IR) spectra of spread monolayers of vinyl octadecanoate have been obtained for a range of surface pressures at 292 K. Unpolarised and s- and p-polarised radiation at 30°angle of incidence have been used. Results in the C-H stretching region show that even at very low surface pressures the monolayer appears to consist of condensed domains where the acyl chains are highly ordered and densely packed. At higher surface pressures the average packing density is higher, but otherwise the spectra are unaltered, showing that the acyl chains remain highly ordered with few gauche bonds throughout the accessible range of surface pressure (0.1 to 18 mN m-1). There was no appreciable change in the spectrum when the monolayer passed through the LC to S phase transition. Copyright (C) 1999 Elsevier Science B.V.