The quasi‐linear theory of plasma oscillations developed by Drummond and Pines, and Vedenov, Velikhov, and Sagdeev is examined in detail using the Bogoliubov‐Krylov technique of nonlinear mechanics. For the particular case treated, the mode coupling terms which were neglected in earlier work are of the same order of magnitude as those kept. The asymptotic time development of the system is also discussed in detail.