Air-liquid interfacial surface tension measurements are reported on four 1-alkyl-3-methylimidazolium ([C-n-mim], n = 2, 4, 6) based ionic liquids at 15 temperatures from (283 to 353) K at atmospheric pressure. To validate the accuracy of the results, the Wilhelmy plate method and the du Nouy ring method were employed in parallel, using the Kruss K100MK2 tensiometer. At each temperature from 29 to 44 individual readings were taken. The surface tension average values at particular temperatures are presented with the estimated overall standard uncertainty ranging from (+/- 0.025 to +/- 0.1) mN . m(-1). An empirical surface tension-temperature equation has been developed describing the temperature dependence of each ionic liquid surface tension. Some details of the measurement procedure that have been found to be important in achieving the highest possible accuracy are discussed. (C) 2009 Elsevier Ltd. All rights reserved.