  In analyzing neutrino oscillation experiments it is often assumed that while
new physics contributes to neutrino masses, neutrino interactions are given by
the Standard Model. We develop a formalism to study new physics effects in
neutrino interactions using oscillation experiments. We argue that the notion
of branching ratio is not appropriate in this case. We show that a neutrino
appearance experiment with sensitivity to oscillation probability
$P_{ij}^{exp}$ can detect new physics in neutrino interactions if its strength
$G_N$ satisfies $(G_N/G_F)^2 \sim P_{ij}^{exp}$. Using our formalism we show
how current experiments on neutrino oscillation give bounds on the new
interactions in various new physics scenarios.
