Many methods are known for the estimation of the orientational order parameter in the nematic phase of a liquid crystal. The order parameter can be calculated directly from a macroscopic quantity measured in the experiment. The birefringence technique has been exploited for the evaluation of order parameter in the nematic phase along with the density measurements which are needed for the calculation of molecular polarizabilities of the molecule. Density and birefringence studies are carried out on four compounds viz., N-(p-n-octyloxybenzylidene)-p-n-propyloxy, butyloxy, hexyloxy and heptyloxy anilines, 8O.O3, 8O.O4, 8O.O6 and 8O.O7. The order parameter is obtained from the molecular polarizabilities obtained using two different internal field models due to Vuks and Neugebauer and the molecular anisotropy calculated using Lippincott delta-function model. The results reveal that both the models agree very near to the isotropic-nematic transition and diverge as nematic field stabilizes. Further, the results are compared with those obtained using Haller's extrapolation technique.