[en] We use the techniques of an effective field theory for heavy quark systems to calculate inclusive lepton energy distributions in heavy meson decays. Our approach is patterned after the operator product expansion analysis of R in e⁺-e^- annihilation and deep inelastic electroproduction. We extend the idea of an operator product expansion to a situation in which we match the physics from a T-product in the high energy theory to a set of local operators in the low energy effective heavy quark field theory. In leading order we reproduce the results of the parton model, but we can also describe the corrections systematically. We are led to the rather surprising conclusion that there are no nonperturbative corrections of order m_bΛ_QCD to the average invariant mass-squared of the final hadronic state. (orig.)