  A detailed study of the solar neutrino vacuum oscillation was made taking
into account three neutrino flavours and the seasonal effect. This analysis was
established for a range of the mixing parameter sin^2(2\phi), that is concerned
with the electron-tau neutrino oscillations, from 0 to 1. We obtained the
allowed mass regions versus mixing angles by fitting only the rates of the five
solar neutrino detectors in activity and we compared with the fits including
the recoil-electron spectrum of the Kamiokande and Super-Kamiokande
experiments. The averaged survival probabilities for electron neutrinos as a
function of the neutrino energy are also obtained, showing that the solutions
for sin^2(2\phi) greater than 0.50 with the maximum exclusion of Be7 neutrinos
and the minimum exclusion of pp neutrinos give a better explanation for the
suppression rates of all detectors.
