In reply to tony:
North on Banbury road or head west to the canal towpath then north to Godstow rd in wolvercote (or off the wolvercote roundabout if coming up Banbury rd.
Carry in through wolvercote till you get to the trout inn then take the Thames path south to the marina, crossing theriver into port meadow. You can the cross the meadow, and head back through Jericho to ban rd. You can extend by adding in a loop of portmeadow, Burgess fields, university parks.
I also used to run into the meadow, through burgess field and out the top to cross the meadow north to wolvercote then rerun as described above. Happy running.