  We performed NLO QCD fit of combined SLAC/BCDMS/NMC DIS data at high $x$.
Model independent x-shape of high twist contribution to structure function
$F_L$ is extracted. Twist-4 contribution is found to be in fair agreement with
the predictions of infrared renormalon model. Twist-6 contribution exhibits
weak tendency to negative values, although in the whole is compatible with zero
within errors.
