We propose a simple closed-form expression relating v(12)(r)-the mean relat
ive velocity of pairs of galaxies at fixed separation r-to the two-point co
rrelation function of mass density fluctuations, xi(r). Our Ansatz is an in
terpolation between the perturbative and stable clustering expressions for
v(12). We compare our analytic model for v(12)(r) with N-body simulations a
nd find excellent agreement in the entire dynamical range probed by the sim
ulations (0.1 less than or similar to xi less than or similar to 1000). Our
results can be used to estimate the cosmological density parameter, Omega,
directly from redshift-distance surveys.