  There is evidence for the existence of massive planets at orbital radii of
several hundred AU from their parent stars where the timescale for planet
formation by core accretion is longer than the disc lifetime. These planets
could have formed close to their star and then migrated outwards. We consider
how the transfer of angular momentum by viscous disc interactions from a
massive inner planet could cause significant outward migration of a smaller
outer planet. We find that it is in principle possible for planets to migrate
to large radii. We note, however, a number of effects which may render the
process somewhat problematic.
