Gibbs ensemble Monte Carlo (GEMC) simulations were used to estimate the orthobaric densities and critical points of two branched alkane series: the 2-methylalkanes and the 2,2-dimethylalkanes, using the recently proposed Nath, Escobedo, and de Pablo revised force field (NERD) [Nath et al., J. Chem. Phys. 108 (1998) 9905; Nath and de Pablo, Mol. Phys. 98 (2000) 231; Nath and Khare, J. Chem. Phys. 115 (2001) 10837]. Vapour-liquid coexistence curves were constructed for molecules containing up to 16 carbon atoms with very good correspondence to experimental data where it is currently available. Critical temperature, T-c, and critical density, rho(c), values were also estimated from this data and compared with predictions from empirical correlations and group contribution methods. (C) 2003 Elsevier Science B.V. All rights reserved.