Includes:
-letter from Humphrey Ocean, artist, to Pete Clark, Evening Standard, dated 12 December 1997, concerning his art and exhibitions
-three letters from Robin Ollington, c2008-28 March 2013, concerning National Service, and the possibility of Sewell writing a foreword to an article
-two letters and a card from Stanley Olson, writer, dated 3 October 1980 and 10 January 1984, containing information on various artists
-letter from Julia Trevelyan Oman, dated 3 March 1982, thanking Sewell for his letter of sympathy on the death of her father
-letter from Barry O'Meara, nephew-in-law of John Vere Brown, artist and photographer, dated 14 December 2005, concerning the artist's paintings
-letter from Simon O'Meara, great nephew of John Vere Brown, artist and photographer, dated 11 August 2000, concerning items belonging to his great uncle
-letter from Sewell to Roger Ormisher, dated 17 April 1994, concerning inaccuracies in an article
-three letters from Richard Ormond, writer, dated 4 June 1982-29 September 1997, concerning a catalogue raisonne of John Singer Sargent
-letter from Mark Ottaway, journalist, dated 9 January 2003, concerning Sewell's work
-letter from Graham Ovenden, artist, undated, praising Sewell's comments regarding contemporary art
-letter from Martin Oxley, artist, undated, thanking Sewell for visiting his show