Two-dimensional packing of linear hydrocarbon chains silylized on thermally oxidized silicon surface with octadecyltrichlorosilane (OTS) was examined by atomic force microscopy in aqueous media. Each alkyl chain planted on SiO2 at 5 degrees C occupies the area 0.227 +/- 0.015 nm(2), which is the value close to the area of 0.19 nm(2) observed for a hydrocarbon chain at the surface of an alkane single crystal.