The thermal behaviour and morphology of a series of homogeneous ethylene-1-octene copolymers, covering a wide range of 1-octene content up to 44 mole%, is studied using differential scanning calorimetry (DSC), time-resolved small-angle X-ray scattering (SAXS) and wide-angle X-ray diffraction (WAXD). The influence of the comonomer (1-octene) content, as well as the influence of the comonomer type (branch length) are investigated by comparison with previous results on homogeneous ethylene-propylene and ethylene-l-butene copolymers. Special emphasis is put on copolymers with high comonomer contents or low densities (<870 kg/m(3)) at room temperature. The thermal behaviour and the morphology of the present copolymers reveal no discontinuities with increasing comonomer content and support a model in which the morphology changes gradually from a lamellar base morphology into a granular one consisting of small blocky structures and, possibly via fringed-micelles, into a morphology consisting of loosely packed ethylene sequences. The latter structures are too small and/or too imperfect to be detected by WAXD. However, SAXS and DSC are sensitive to them and are useful techniques over the whole comonomer content range. (C) 2000