  High statistics fixed target and ISR inclusive photon production data are
compared to next-to-leading order (NLO) QCD calculations. The dependence of the
theoretical predictions on the structure functions, and on the theoretical
scales is investigated. It is shown that the data cannot be simultaneously
fitted with a single set of structure functions and scales. However, it is
argued that as long as one restricts the data/theory comparison to the xT range
where the theory is reliable, i.e. stable with respect to the scale variation,
there is no need to introduce an additional primordial kT dependence except for
Be data. Finally a precise determination of the strong coupling constant,
alpha_s, is performed from the direct photon production cross sections obtained
in high statistics pbar p and pp collisions at the CERN SPS (UA6) by a NLO QCD
analysis.
