  Using an Eulerian perturbative calculation, we show that the distribution of
relative pairwise velocities which arises from gravitational instability of
Gaussian density fluctuations has asymmetric (skewed) exponential tails. The
negative skewness is induced by the negative mean streaming velocity of pairs
(the infall prevails over expansion), while the exponential tails arise because
the relative pairwise velocity is a number, not volume weighted statistic. The
derived probability distribution is compared with N-body simulations and shown
to provide a reasonable fit.
