  All existing ``positive'' results on two neutrino double beta decay in
different nuclei were analyzed. Using the procedure recommended by the Particle
Data Group, weighted average values for half-lives of $^{48}$Ca, $^{76}$Ge,
$^{82}$Se, $^{96}$Zr, $^{100}$Mo, $^{100}$Mo - $^{100}$Ru ($0^+_1$),
$^{116}$Cd, $^{130}$Te, $^{150}$Nd, $^{150}$Nd - $^{150}$Sm ($0^+_1$) and
$^{238}$U were obtained. Existing geochemical data were analyzed and
recommended values for half-lives of $^{128}$Te, $^{130}$Te and $^{130}$Ba are
proposed. We recommend the use of these results as presently the most precise
and reliable values for half-lives.
