  The difference of vector and axial-vector charged current correlators is
analyzed by means of QCD sum rules. The contribution of 10-dimensional 4-quark
condensates is calculated and its value is estimated within the framework of
factorization hypothesis. It is compared to the result, obtained from operator
fit of Borel sum rules in the complex q^2-plane, calculated from experimental
data on hadronic tau-decays. This fit gives accurate values of the light quark
condensate and quark-gluon mixed condensate. The size of the high-order
operators and the convergence of operator series are discussed.
