Pyridinium-based cations are the second most frequently occurring cations in the commonly studied ionic liquid mixtures - a new prospective field just opened for the property tuning of substances of practical use. To this purpose, a sufficiently accurate knowledge of the properties of pure components is necessary. Presented here are results of a study of the surface tension and 0.1 MPa densities for members of four homologous series consisting of a 1-alkyl-pyridinium or 1-alkyl-m-methylpyridinium cation with m = 2, 3, or 4 and of the bis(trifluoromethylsulfonyl)imide anion. Empirical models are presented, based on the parachor and group contribution approach, which generate recommended surface tension and 0.1 MPa density values for ionic liquids from the studied homologous series including those for which no experimental data are available. The models have been developed both on the basis of data from the literature and on our own data for four ionic liquids with a pyridinium-based cation bearing a propyl side-chain, yet studied poorly in those two respects or even not at all. The presented density data were measured using the buoyancy method with an estimated combined expanded uncertainty at the 0.95 level of confidence U-c = 0.8 kg m(-3) (6.10(-4)0) at the most. The du Nouy ring method and the Wilhelmy plate method were used to obtain the data on the surface tension with U-c near (0.2 and 0.05) m(-1) respectively. The surface tension and buoyancy forces were measured at temperatures from (263 to 365) K using the Kruss K100 Mk2 tensiometer. The deviation of the recommended surface tension and density values from their true values is estimated not to exceed 0.3 mN m(-1) and 0.15%, respectively. (C) 2016 Elsevier B.V. All rights reserved.