  We observed the Seyfert I active galaxy/broad line radio galaxy 3C120 with
the Chandra high energy transmission gratings and present an analysis of the
soft X-ray spectrum. We identify the strongest absorption feature (detected at
>99.9% confidence) with O VIII Lya (FWHM=1010^{+295}_{-265} km/s), blueshifted
by -5500 +/- 140 km/s from systemic velocity. The absorption may be due to
missing baryons in warm/hot intergalactic medium (WHIGM) along the
line-of-sight to 3C 120 at z=0.0147 +/- 0.0005, or it could be intrinsic to the
jet of 3C 120. Assuming metallicities of 0.1 solar, we estimate an ionic column
density of N_{O VIII}>3.4 \times 10^{16} cm^{-2} for WHIGM and a filament depth
of <19 h^{-1}_{70} Mpc. We find a baryon overdensity >56 relative to the
critical density of a $\Lambda$-dominated cold dark matter universe, which is
in reasonable agreement with WHIGM simulations. We detect, at marginal
significance, absorption of O VIII Lya at z\sim 0 due to a hot medium in the
Local Group. We also detect an unidentified absorption feature at \sim 0.71
keV. Absorption features which might be expected along with O VIII Lya, were
not significant statistically. Relative abundances of metals in the WHIGM and
local absorbers may therefore be considerably different from solar.
