  We have discovered a third quasar absorption system which is consistent with
a low deuterium to hydrogen abundance ratio, D/H = 3.4 times 10^-5. The z ~ 2.8
partial Lyman limit system towards QSO 0130-4021 provides the strongest
evidence to date against large D/H ratios because the H I absorption, which
consists of a single high column density component with unsaturated high order
Lyman series lines, is readily modeled -- a task which is more complex in other
D/H systems. We have obtained twenty-two hours of spectra from the HIRES
spectrograph on the W.M. Keck telescope, which allow a detailed description of
the Hydrogen. We see excess absorption on the blue wing of the H I Lyman alpha
line, near the expected position of Deuterium. However, we find that Deuterium
cannot explain all of the excess absorption, and hence there must be
contamination by additional absorption, probably H I. This extra H I can
account for most or all of the absorption at the D position, and hence D/H = 0
is allowed. We find an upper limit of D/H < 6.7 times 10^-5 in this system,
consistent with the value of D/H ~ 3.4 times 10^-5 deduced towards QSO
1009+2956 and QSO 1937-1009 by Burles and Tytler (1998a, 1998b). This
absorption system shows only weak metal line absorption, and we estimate [Si/H]
< -2.6 -- indicating that the D/H ratio of the system is likely primordial. All
four of the known high redshift absorption line systems simple enough to
provide useful limits on D are consistent with D/H = 3.4 +/- 0.25 times 10^-5.
Conversely, this QSO provides the third case which is inconsistent with much
larger values.
