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We have conducted a systematic survey for intervening OVI absorbers inavailable echelle spectra of 16 QSOs at z_QSO = 0.17-0.57. These spectra wereobtained using HST/STIS with the E140M grating. Our search uncovered a total of27 foreground OVI absorbers with rest-frame absorption equivalent widthW_r(1031) > 25mA. Ten of these QSOs exhibit strong OVI absorbers in theirvicinity. Our OVI survey does not require the known presence of Lya, and theechelle resolution allows us to identify the OVI absorption doublet based ontheir common line centroid and known flux ratio. We estimate the total redshiftsurvey path, \Delta z, using a series of Monte-Carlo simulations, and find that\Delta z=1.66, 2.18, and 2.42 for absorbers of strength W_r = 30, 50 and 80mA,respectively, leading to a number density of dN(W > 50mA)/dz = 6.7 +/- 1.7 anddN(W > 30mA)/dz = 10.4 +/- 2.2. In contrast, we also measure dN/dz = 27 +/- 9for OVI absorbers of W_r > 50mA at |\Delta v|< 5000 kms from the backgroundQSOs. Using the random sample of OVI absorbers with well characterized surveycompleteness, we estimate a mean cosmological mass density of the OVI gas\Omega(OVI)h = 1.7 +/- 0.3 x 10^-7. In addition, we show that <5% of OVIabsorbers originate in underdense regions that do not show a significant traceof HI. Furthermore, we show that the neutral gas column N(HI) associated withthese OVI absorbers spans nearly five orders of magnitude, and show moderatecorrelation with N(OVI). Finally, while the number density of OVI absorbersvaries substantially from one sightline to another, it also appears to beinversely correlated with the number density of HI absorbers along individuallines of sight.

A STIS Survey for OVI Absorption Systems at 0.12 < z < 0.5 I.: The Statistical Properties of Ionized Gas