The differential cross section d sigma/d sum E^jet_T has been
measured for events with total transverse energy sum E^jet_T > 320 GeV.  The
results are based on 112 pb^-1 of ppbar collisions at sqrt s = 1.8 TeV
collected with the Collider Detector at Fermilab at the Tevatron collider.
The data are compared with QCD predictions using various sets of parton
distribution functions.  The observed cross section at the highest values of
total transverse energy is higher than current predictions based on
O(alpha^3_s) perturbative QCD calculations.  The apparent excess is reduced
when a new parton distribution function set is used for the QCD predictions.
This set was derived in order to reduce a similar excess observed in the
inclusive jet cross sections at high jet transverse energies.