What I am playing now is the second disc of the CD set "Two Sides, the very best of Mike Oldfield."
Guilty and The Song of the Sun have lots of surround.
Family Man, Summit Day, and Angelique have small amounts of surround.
Five Miles Out, Magic Touch, Heaven's Open, Tattoo (from Tubular Bells 2), and Amber Light* start with no surround, but surround you at the very end.
Moonlight Shadow, Shadow on the Wall, To France, Etude, Islands, Lake Constance*, Broad Sunlit Uplands*, The Doge's Palace*, and On My Heart haves almost no surround.
* Part of The Millennium Bell
Tattoo is a different recording from the one in Tubular Bells 2.
I think the large variance of surround content comes from the wide variation of record contracts and purposes of the music.