  The optimal conformal mapping of the Borel plane was recently used to
accelerate the convergence of the perturbation expansions in QCD. In this work
we discuss the relevance of the method for the calculation of the Laplace-Borel
integral expressing formally the QCD Green functions. We define an optimal
expansion of the Laplace-Borel integral in the principal value prescription and
establish conditions under which the expansion is convergent.
