  We present an improved measurement of the eta' meson energy spectrum in
Upsilon(1S) decays, using 1.2 fb^{-1}} of data taken at the Upsilon(1S)
center-of-mass energy with the CLEO III detector. We compare our results with
models of eta' gluonic form factor that have been suggested to explain the
unexpectedly large B to eta' X_s rate. Models based on perturbative QCD fail to
fit the data for large eta' energies, showing that Standard Model strong
interaction dynamics is not likely to provide an explanation for the large rate
of high energy eta' observed in B decays.
