  We report the discovery of six new substellar companions of main-sequence
stars, detected through multiple Doppler measurements with the instrument HARPS
installed on the ESO 3.6m telescope, La Silla, Chile. These extrasolar planets
are orbiting the stars BD -17 0063, HD 20868, HD 73267, HD 131664, HD 145377,
HD 153950. The orbital characteristics which best fit the observed data are
depicted in this paper, as well as the stellar and planetary parameters. Masses
of the companions range from 2 to 18 Jupiter masses, and periods range from 100
to 2000 days. The observational data are carefully analysed for
activity-induced effects and we conclude on the reliability of the observed
radial-velocity variations as of exoplanetary origin. Of particular interest is
the very massive planet (or brown-dwarf companion) around the metal-rich HD
131664 with M2sini= 18.15 MJup, and a 5.34-year orbital period. These new
discoveries reinforces the observed statistical properties of the exoplanet
sample as known so far.
