  We have performed a detailed phenomenological investigation of the hard
colour singlet exchange process which is observed at the Tevatron in events
which have a large rapidity gap between outgoing jets. We include the effects
of multiple interactions to obtain a prediction for the gap survival factor.
Comparing the data on the fraction of gap events with the prediction from BFKL
pomeron exchange we find agreement provided that a constant value of alpha_s is
used in the BFKL calculation. Moreover, the value of alpha_s is in line with
that extracted from measurements made at HERA.
