In this paper, a sixth-order spatially accurate and fourth-order temporally accurate finite-difference scheme is employed to study a spatially developing mixing layer. We examine the spatial growth rate of the boundary layer, its dependence on density and velocity ratios and compare our results with experimental trends reported in the literature. We show that as surmised by other workers and also experimentally found, that rate of growth of the mixing layer is proportional to the ratio of the difference of the velocities in the two streams normalized by the sum of the velocities in the two streams.