This is part 6 of a series of contributions by the critical properties group of the IUPAC Commission 1.2 on Thermodynamics, Subcommittee on Thermodynamic Data. It presents all known experimental data for the critical constants of unsaturated aliphatic hydrocarbons, which have been divided into five families : linear alk-1-enes (10 compounds, C-2 to C-12); other alkenes (8 compounds, C-4 to C-8); alkadienes (3 compounds, C-3 to C-6); terpenes (3 C-10 compounds); and alkynes (3 compounds, C-2 to C-4). Recommendations are given together with uncertainties. Critical temperatures have been converted to ITS-90.