  We re-examine the matter neutrino oscillation probabilities considering the
decoherence phenomenon as a sub-leading effect. In this paper we point out the
relevance of having the correct interpretation of the decoherence matrix in the
different quantum bases, within the framework of neutrino oscillation
probabilities in matter. Based on this treatment we develop an analytical
formula for matter neutrino oscillation probabilities for three generations,
with a range of application up to the decoherence parameter $\Gamma \sim
10^{-23}$ GeV. We observe that, due to decoherence, the amplitudes of the
neutrino/antineutrino oscillation probabilities increase in an energy
independent way. We also find that decoherence can reduce the absolute value of
the CP asymmetry, relative to its value at the pure oscillation case. As a side
effect we have found a degeneracy between the decoherence parameter $\Gamma$
and the CP violation phase $\delta$.
