The critical pressures and the critical temperatures of 1-methylnaphthalene, 2-methylnaphthalene, 1,3-dimethylnaphthalene, 1,4-dimethylnaphthalene, 2-ethylnaphthalene have been measured. All the alkylnaphthalenes investigated decompose at near-critical temperatures. A pulse-heating method applicable to measuring the critical properties of thermally unstable compounds has been used. The times of heating from the beginning of a pulse to the moment of reaching the critical temperature were from 0.03 to 0.46 ms. The short residence times provided little degradation of the substances in the course of the experiments. Comparisons with experimental results of other workers have been presented. The experimental critical constants of alkylnaphthalenes have been compared with those calculated by the group-contribution methods of Wilson and Jasperson and Marrero and Gani. (C) 2013 Elsevier B.V. All rights reserved.