Sulfur-based bidentate ligands are active in Cr-catalysed selective ethylene oligomerisation but generally produce large amounts of solids. Through a systematic process condition optimisation study, the amount of solids formed with two P,S-bidentate ligands was reduced from 88% and 57% to 13% and 6% respectively, while maintaining reasonable oligomerisation activities and achieving high liquid product selectivities (> 50% 1octene and > 75% 1-hexene and 1-octene combined). The selective suppression of solids formation indicated that ethylene oligomerisation and polymerisation reactions are possibly facilitated by different catalytic species.