  We calculate perturbative Wilson loops of various sizes up to loop order
$n=20$ at different lattice sizes for pure plaquette and tree-level improved
Symanzik gauge theories using the technique of Numerical Stochastic
Perturbation Theory. This allows us to investigate the behavior of the
perturbative series at high orders. We observe differences in the behavior of
perturbative coefficients as a function of the loop order. Up to $n=20$ we do
not see evidence for the often assumed factorial growth of the coefficients.
Based on the observed behavior we sum this series in a model with
hypergeometric functions. Alternatively we estimate the series in boosted
perturbation theory. Subtracting the estimated perturbative series for the
average plaquette from the non-perturbative Monte Carlo result we estimate the
gluon condensate.
