  The uncertainty in the calculation of many important new processes at the
Tevatron and LHC is dominated by that concerning the gluon distribution
function. We investigate the uncertainty in the gluon distribution of the
proton by systematically varying the gluon parameters in the global QCD
analysis of parton distributions. The results depend critically on the parton
momentum fraction x and the QCD scale Q^2. The uncertainties are presented for
integrated gluon-gluon and gluon-quark luminosities for both the Tevatron and
LHC as a function of sqrt(tau)=sqrt(x1x2)=sqrt(shat/s), the most relevant
quantity for new particle production. The uncertainties are reasonably small,
except for large x.
