  We use Hubble Space Telescope (HST)/ Space Telescope Imaging Spectrograph
(STIS) long-slit G430M and G750M spectra to analyse the extended [O~III] 5007A
emission in a sample of twelve nearby (z < 0.12) luminous (L_bol > 1.6 x 10^45
erg s^-1) QSO2s. The purpose of the study is to determine the properties of the
mass outflows of ionised gas and their role in AGN feedback. We measure fluxes
and velocities as functions of radial distances. Using Cloudy models and
ionising luminosities derived from [O~III] 5007A, we are able to estimate the
densities for the emission-line gas. From these results, we derive masses of
[O~III]-emitting gas, mass outflow rates, kinetic energies, kinetic
luminosities, momenta and momentum flow rates as a function of radial distance
for each of the targets. For the sample, masses are several times 10^3 - 10^7
solar masses and peak outflow rates are 9.3 x 10^-3 Msun/yr to 10.3 Msun/yr.
The peak kinetic luminosities are 3.4 x 10^-8 to 4.9 x 10^-4 of the bolometric
luminosity, which does not approach the 5.0 x 10^-3 - 5.0 x 10^-2 range
required by some models for efficient feedback. For Mrk 34, which has the
largest kinetic luminosity of our sample, in order to produce efficient
feedback there would have to be 10 times more [O~III]-emitting gas than we
detected at its position of maximum kinetic luminosity. Three targets show
extended [O~III] emission, but compact outflow regions. This may be due to
different mass profiles or different evolutionary histories.
