  GX 9+9 (4U 1728-16) is a low mass X-ray binary (LMXB) source harboring a
neutron star. Although it belongs to the subclass of the bright Atoll sources
together with GX 9+1, GX 3+1, and GX 13+1, its broadband spectrum is poorly
studied and apparently does not show reflection features in the spectrum.
  To constrain the continuum well and verify whether a relativistic smeared
reflection component is present, we analyze the broadband spectrum of GX 9+9
using {\it BeppoSAX} and \textit{XMM-Newton} spectra covering the 0.3-40 keV
energy band.
  We fit the spectrum adopting a model composed of a disk-blackbody plus a
Comptonized component whose seed photons have a blackbody spectrum (Eastern
Model). A statistically equivalent model is composed of a Comptonized component
whose seed photons have a disk-blackbody distribution plus a blackbody that
mimics a saturated Comptonization likely associated with a boundary layer
(Western model). Other trials did not return a good fit.
  The spectrum of GX 9+9 was observed in a soft state and its luminosity is
$2.3 \times 10^{37}$ erg s$^{-1}$ assuming a distance to the source of 5 kpc.
In the Eastern Model scenario, we find the seed-photon temperature and electron
temperature of the Comptonized component to be $1.14^{+0.10}_{-0.07}$ keV and
$2.80^{+0.09}_{-0.04}$ keV, respectively, while the optical depth of the
Comptonizing corona is $8.9\pm0.4$. The color temperature of the inner
accretion disk is $0.86^{+0.08}_{-0.02}$ keV and $0.82 \pm 0.02$ keV for the
{\it BeppoSAX} and \textit{XMM-Newton} spectrum, respectively. In the Western
Model scenario, instead, we find that the seed-photon temperature is $0.87 \pm
0.07$ keV and $1.01 \pm 0.08$ keV for the {\it BeppoSAX} and
\textit{XMM-Newton} spectrum, respectively. (Abridged abstract)
