Kinetics of phase separation in a three-dimensional single-component Lennard-Jones fluid, that exhibits vapor-liquid transition, is studied via molecular dynamics simulations after quenching homogeneous systems, of different overall densities, inside the coexistence region. For densities close to the vapor branch of the coexistence curve, phase separation progresses via nucleation of liquid droplets and collisions among them. This is different from the evaporation-condensation mechanism proposed by Lifshitz and Slyozov, even though both lead to power-law growth of average domain size, as a function of time, with an exponent α = 1∕3. Beyond a certain threshold value of the overall density, we observe elongated, percolating domain morphology which suddenly enhances the value of α. These results are consistent with some existing theoretical expectations.