  We present a preliminary determination of the CKM matrix element |Vub| based
on the analysis of semileptonic B decays from a sample of 88 million
Upsilon(4S) decays collected with the BaBar detector at the e+e- storage ring.
Charmless semileptonic B decays are selected using the electron energy E_e and
the invariant mass q^2 of the electron-neutrino pair. The neutrino momentum is
inferred from a measurement of the visible energy and momentum in the detector
and knowledge of the e+e- beam momenta. The partial branching fraction is
determined in a region of the q^2-E_e plane where semileptonic B decays to
charm are highly suppressed. The total charmless semileptonic branching
fraction is extracted using a theoretical calculation based on the heavy quark
expansion. Preliminary results yield |Vub| = (4.57 +/- 0.21 +/- 0.25 +/- 0.34
+0.59/-0.29 +/- 0.22) x 10^{-3} where the uncertainties are from statistics
(data and MC), detector modeling, background modeling, the shape function, and
the heavy quark operator product expansion, respectively.
