  A description of neutrino oscillation phenomena is presented which is based
on relativistic quantum mechanics and includes both entangled state and source
dependent aspects, unlike both of the conventional approaches which use either
equal energies or equal momenta for the different neutrino mass eigenstates. To
second order in the neutrino masses, the standard result is recovered thus
showing an absence of source dependence to this order. The time dependence of
the wavefunction is found to be crucial to recovering the conventional result.
An ambiguity appears at fourth order in the neutrino masses which generally
leads to source dependence, but the standard formula can be promoted to this
order by a plausible convention.
