| 1 | O Thiam Chin | Fox Fire Girl | | NOVEL | 9781912098644 | 2017-03-01 | 2018-05-03 | £10.00 |
| 2 | O Thiam Chin | Now That It's Over | | NOVEL | 9781912098699 | 2016-06-01 | 2017-05-01 | £10.00 |
| 3 | Fitz-James O'Brien | The Collected Supernatural and Weird Fiction of Fitz-James O'Brien | The Collected Supernatural and Weird Fiction of | COLLECTION | 9781782826620 | 2017-09-05 | 2017-09-05 | £21.99 |
| 4 | Fitz-James O'Brien | The Diamond Lens and Other Stories | | COLLECTION | 9781843913580 | 2011-11-30 | 2012-03-30 | £8.00 |
| 5 | Kiera O'Brien | Millie vs the Machines | Millie | NOVEL | 9781848668430 | 2015-08-06 | 2015-08-06 | £2.99 |
| 6 | Kiera O'Brien | Millie vs the World | Millie | NOVEL | 9781848668492 | 2016-05-19 | 2016-05-19 | £3.49 |
| 7 | Elliott O'Donnell | Casebook of Ghosts | | NOVEL | None on record | 1971-01-01 | 1971-01-01 | £0.50 |
| 8 | Elliott O'Donnell | Casebook of Ghosts Volume Two | | NOVEL | None on record | 1971-03-01 | 1971-03-01 | £0.25 |
| 9 | Paraic O'Donnell | The House on Vesper Sands | | NOVEL | 9781474600392 | 2018-10-18 | 2018-10-18 | £14.99 |
| 10 | Mike O'Driscoll | Eyepennies | ? | CHAPBOOK | 9780955368356 | 2012-11-01 | 2012-11-01 | £5.99 |
| 11 | Marjorie O'Hara | The Cunning Man's Glass | | NOVEL | 0749702982 | 1989-01-01 | 1990-01-01 | £2.50 |
| 12 | Patrick O'Leary | The Black Heart | | COLLECTION | 9781906301811 | 2009-09-01 | 2009-10-01 | £35.00 |
| 13 | Daniel O'Mahony | Cabinet of Light | ? | CHAPBOOK | 9781845831424 | 2020-02-29 | 2020-02-29 | £8.99 |
| 14 | Daniel O'Mahony | Falls the Shadow | Doctor Who New Adventures | NOVEL | 0426204271 | 1994-11-01 | 1994-11-01 | £4.99 |
| 15 | Daniel O'Mahony | Force Majeure | | NOVEL | 9781845830502 | 2007-08-01 | 2007-08-01 | £7.99 |
| 16 | Daniel O'Mahony | The Cabinet of Light | ? | CHAPBOOK | 1903889189 | 2003-07-01 | 2003-07-01 | £10.00 |
| 17 | Daniel O'Mahony | The Man In The Velvet Mask | Doctor Who Missing Adventures | NOVEL | 0426204611 | 1996-02-01 | 1996-02-01 | £4.99 |
| 18 | Anthony O'Neill | Scheherezade | | NOVEL | 0747265283 | 2001-01-01 | 2002-07-01 | £6.99 |
| 19 | Dave O'Neill | Find the Lady | ? | CHAPBOOK | None on record | 2019-03-27 | 2019-03-27 | £0.99 |
| 20 | Ian O'Neill | Green-Jack and the Heritage Bloodstone | | NOVEL | 9780755207039 | 2012-07-13 | 2012-07-13 | £8.99 |
| 21 | Joanna O'Neill | A World Invisible | | NOVEL | 9780956443205 | 2008-03-01 | 2010-01-01 | £7.99 |
| 22 | Joanna O'Neill | The Stranger Bookshop | | NOVEL | 9780956443267 | 2014-02-24 | 2014-02-24 | £8.99 |
| 23 | Marie O'Regan | A Carnivàle of Horror: Dark Tales from the Fairground | | ANTHOLOGY | 9781848635043 | 2012-10-01 | 2012-10-01 | £39.99 |
| 24 | Marie O'Regan | The British Fantasy Society: A Celebration | | ANTHOLOGY | 0953868168 | 2006-01-01 | 2006-10-01 | £11.99 |
| 25 | Jane O'Reilly | Blue Shift | The Second Species Trilogy | NOVEL | 9780349416588 | 2017-06-01 | 2017-10-05 | £8.99 |
| 26 | Tony O'Reilly | Sentinel | | NOVEL | 1905108346 | 2006-11-27 | 2006-11-27 | £8.99 |
| 27 | Patti O'Shea | Vampire Hunter | | ANTHOLOGY | 9781472006813 | 2013-10-04 | 2013-10-01 | £6.98 |
| 28 | Vincent O'Sullivan | Master of Fallen Years: Complete Supernatural Stories of Vincent O'Sullivan | | COLLECTION | 0952049287 | 1995-01-01 | 1995-01-01 | £24.00 |
| 29 | Chris Oakley | The Legend of Perseus | | NOVEL | 0951457101 | 1989-01-01 | 1989-01-01 | £3.50 |
| 30 | Joyce Carol Oates | Rape: A Love Story | | NOVEL | 9781782395256 | 2004-11-30 | 2014-06-12 | £6.49 |
| 31 | Silvina Ocampo | The Topless Tower | | NOVEL | 9781843918554 | 2010-05-28 | 2010-05-28 | £8.99 |
| 32 | John October | The Anarchy Pedlars | | NOVEL | 0709156839 | 1976-01-01 | 1976-01-01 | £3.10 |
| 33 | Mel Odom | Redemption | Angel | NOVEL | 0671041460 | 2000-06-01 | 2000-06-01 | £5.99 |
| 34 | David Ogilvy | Escape from Jupiter | | NOVEL | 0563404302 | 1994-01-01 | 1995-05-01 | £3.99 |
| 35 | Ian Ogilvy | Measle and the Doompit | Measle Stubbs | NOVEL | 9780192726230 | 2007-09-01 | 2008-06-05 | £5.99 |
| 36 | Ian Ogilvy | The Monster of Mucus! | | NOVEL | 9780192729736 | 2006-09-07 | 2011-02-01 | £5.99 |
| 37 | Miikko Oikkonen | Nymphs | | NOVEL | 9781472213280 | 2015-08-27 | 2016-01-28 | £8.99 |
| 38 | Miikko Oikkonen | Nymphs Part I: Full Moon Rising | ? | CHAPBOOK | 9781472232946 | 2015-06-01 | 2015-06-01 | £1.99 |
| 39 | Miikko Oikkonen | Nymphs Part II: Darkness Falls | ? | CHAPBOOK | 9781472232977 | 2015-06-16 | 2015-06-16 | £1.99 |
| 40 | Irenosen Okojie | Butterfly Fish | | NOVEL | 9781909762145 | 2015-06-25 | 2016-12-19 | £0.99 |
| 41 | Irenosen Okojie | Nudibranch | | COLLECTION | 9780349700922 | 2019-11-07 | 2019-11-07 | £14.99 |
| 42 | Nnedi Okorafor | Long Juju Man | ? | CHAPBOOK | 9780230722071 | 2009-03-01 | 2009-03-01 | £5.35 |
| 43 | Ben Okri | Astonishing the Gods | | NOVEL | 9781784081836 | 1995-01-01 | 2014-10-09 | £7.99 |
| 44 | Ben Okri | Starbook | | NOVEL | 9781846040818 | 2007-08-16 | 2008-07-03 | £8.99 |
| 45 | Jenny Oldfield | Silver Cloud | Dream Seeker | NOVEL | 0340851082 | 2002-03-01 | 2002-03-01 | £4.99 |
| 46 | Jenny Oldfield | Wings of Icarus | ? | CHAPBOOK | 9780713684193 | 2007-09-01 | 2007-09-01 | £4.99 |
| 47 | Pamela Oldfield | Pamela Oldfield's Spine Chillers | | COLLECTION | 0216922402 | 1987-10-01 | 1987-10-01 | £6.95 |
| 48 | June Oldham | The Raven Waits | | NOVEL | 9781444907384 | 1979-01-01 | 2011-09-01 | £3.99 |
| 49 | Trevor Oldham | The Shaman | | NOVEL | 9781847485588 | 2009-05-26 | 2009-05-26 | £5.99 |
| 50 | Nancy Olin | Thorn Abbey | | NOVEL | 9781471117794 | 2013-05-09 | 2013-05-09 | £6.99 |
| 51 | Margaret Oliphant | A Beleaguered City and Other Tales of the Seen and the Unseen | | COLLECTION | 1841950602 | 2000-09-07 | 2000-09-07 | £7.95 |
| 52 | T. E. Olivant | The Lunar Deception | Moon Colony | NOVEL | None on record | 2018-04-03 | 2018-04-03 | £0.99 |
| 53 | T. E. Olivant | The Lunar Pursuit | Moon Colony | NOVEL | None on record | 2018-04-03 | 2018-04-03 | £2.99 |
| 54 | Jana Oliver | Briar Rose | | NOVEL | 9781447241096 | 2013-09-12 | 2013-09-12 | £6.99 |
| 55 | Jana Oliver | The Demon Trappers: Forsaken / Forbidden | Demon Trappers | OMNIBUS | 9781447241744 | 2013-07-04 | 2013-07-04 | £8.99 |
| 56 | Jonathan Oliver | The Call of Kerberos | Silas Morlader | NOVEL | 9781906735289 | 2009-10-15 | 2009-10-15 | £6.99 |
| 57 | Reggie Oliver | Flowers of the Sea: Thirteen Stories and Two Novellas | | COLLECTION | 9781905784639 | 2013-11-05 | 2014-02-17 | £14.95 |
| 58 | Reggie Oliver | Holidays from Hell | | COLLECTION | None on record | 2017-01-30 | 2017-01-30 | £4.99 |
| 59 | Reggie Oliver | Masques of Satan: Twelve Tales and a Novella | | COLLECTION | 9781905784806 | 2007-11-01 | 2016-02-15 | £14.95 |
| 60 | Reggie Oliver | Mrs Midnight and Other Stories | | COLLECTION | 9781905784431 | 2011-09-30 | 2012-01-10 | £14.95 |
| 61 | Reggie Oliver | Shadow Plays | | COLLECTION | 9780957160606 | 2012-03-20 | 2012-03-20 | £30.00 |
| 62 | Reggie Oliver | The Ballet of Dr Caligari & Madder Mysteries | | COLLECTION | 9781912586158 | 2019-07-11 | 2019-07-11 | £14.99 |
| 63 | Reggie Oliver | The Complete Symphonies of Adolf Hitler & Other Strange Stories | | COLLECTION | 0955132908 | 2005-01-01 | 2005-01-01 | £28.50 |
| 64 | Reggie Oliver | The Dreams of Cardinal Vittorini & Other Strange Stories | | COLLECTION | None on record | 2003-01-01 | 2003-01-01 | £35.00 |
| 65 | Lars-Henrik Olsen | Erik and the Gods: Journey to Valhalla | | NOVEL | 9781906582937 | 2017-07-19 | 2017-07-19 | £9.99 |
| 66 | Mark Olshaker | Journey Into Darkness | | NOVEL | 9781787465145 | 2019-10-17 | 2019-10-17 | £8.99 |
| 67 | Danel Olson | Exotic Gothic 4 (Postscripts #28/29) | Postscripts | ANTHOLOGY | 9781848633346 | 2012-07-01 | 2012-07-01 | £59.99 |
| 68 | Danel Olson | Exotic Gothic 5, Volume I | Exotic Gothic | ANTHOLOGY | 9781848636187 | 2013-06-01 | 2013-06-01 | £24.99 |
| 69 | Danel Olson | Exotic Gothic 5, Volume II | Exotic Gothic | ANTHOLOGY | 9781848636194 | 2013-06-01 | 2013-06-01 | £24.99 |
| 70 | Jonathan Edward Ondrashek | Fuck the Rules | | ANTHOLOGY | 9781974328055 | 2017-08-07 | 2017-08-07 | £10.00 |
| 71 | Oliver Onions | Ghost Stories | | COLLECTION | 1872621546 | 2003-05-01 | 2003-05-01 | £30.00 |
| 72 | Oliver Onions | The Dead of Night: The Ghost Stories of Oliver Onions | | COLLECTION | 9781840226409 | 2010-08-15 | 2010-08-15 | £2.99 |
| 73 | Hiawyn Oram | The Totally Terrifying Three | ? | CHAPBOOK | 9781444903027 | 2011-10-06 | 2011-10-06 | £10.99 |
| 74 | Hiawyn Oram | The Totally Terrifying Three | | NOVEL | 9781444923544 | 2014-10-02 | 2014-10-02 | £3.99 |
| 75 | Neil Oram | The Storm's Howling Through Tiflis | The Warp | NOVEL | 0722165528 | 1980-09-01 | 1980-09-01 | £1.75 |
| 76 | Susie Orbach | Fifty Shades of Feminism | | ANTHOLOGY | None on record | 2013-01-01 | 2016-09-01 | £6.99 |
| 77 | Christopher Orland | The Ubiquitous Man: Travel Beyond the Brink | | NOVEL | 9781906791155 | 2008-12-15 | 2008-12-15 | £14.99 |
| 78 | Kate Orman | Blue Box | Doctor Who BBC Past Doctors | NOVEL | 9781448140169 | 2003-03-01 | 2012-03-31 | £2.99 |
| 79 | Kate Orman | Fallen Gods | Doctor Who (Telos) Novellas | NOVEL | 1903889200 | 2003-09-01 | 2003-09-01 | £10.00 |
| 80 | Kate Orman | Return of the Living Dad | Doctor Who New Adventures | NOVEL | 0426204824 | 1996-08-01 | 1996-08-01 | £4.99 |
| 81 | Kate Orman | Seeing I | Doctor Who BBC 8th Doctor | NOVEL | 9781448140145 | 1998-06-01 | 2012-03-31 | £2.99 |
| 82 | Kate Orman | Set Piece | Doctor Who New Adventures | NOVEL | 0426204360 | 1995-02-01 | 1995-02-01 | £4.99 |
| 83 | Kate Orman | Sleepy | Doctor Who New Adventures | NOVEL | 0426204654 | 1996-03-01 | 1996-03-01 | £4.99 |
| 84 | Kate Orman | So Vile a Sin | Doctor Who New Adventures | NOVEL | 0426204840 | 1997-04-01 | 1997-04-01 | £4.99 |
| 85 | Kate Orman | The Left-Handed Hummingbird | Doctor Who New Adventures | NOVEL | 0426204042 | 1993-12-01 | 1993-12-01 | £4.50 |
| 86 | Kate Orman | The Room with No Doors | Doctor Who New Adventures | NOVEL | 0426205006 | 1997-02-01 | 1997-02-01 | £4.99 |
| 87 | Kate Orman | The Year of Intelligent Tigers | Doctor Who BBC 8th Doctor | NOVEL | 9781849901734 | 2001-06-01 | 2012-06-30 | £2.99 |
| 88 | Kate Orman | Unnatural History | Doctor Who BBC 8th Doctor | NOVEL | 9781849901819 | 1999-06-01 | 2011-08-31 | £9.99 |
| 89 | Kate Orman | Vampire Science | Doctor Who BBC 8th Doctor | NOVEL | 056340566X | 1997-07-01 | 1997-07-01 | £4.99 |
| 90 | Kate Orman | Walking to Babylon | Doctor Who New Adventures | NOVEL | 0426205219 | 1997-01-01 | 1998-02-01 | £4.99 |
| 91 | Helen Orme | Vampires Are So Boring | ? | CHAPBOOK | 9781445118130 | 2013-05-09 | 2013-05-09 | £5.99 |
| 92 | Nicola Ormerod | Roxy May: Help My Granda is Haunting Me! | | NOVEL | 9781908505866 | 2011-10-01 | 2011-10-01 | £7.99 |
| 93 | Markus Orths | The Staff Room | | NOVEL | 9781903517550 | 2008-03-27 | 2008-03-27 | £6.99 |
| 94 | Eric Ortlund | Dead Petals: An Apocalypse | | NOVEL | 9781908824295 | 2013-03-22 | 2013-03-22 | £8.99 |
| 95 | George Orwell | Animal Farm / Burmese Days / A Clergyman's Daughter / Coming Up for Air / Keep the Aspidistra Flying / Nineteen Eighty-Four | | OMNIBUS | 0706405676 | 1976-01-01 | 1976-01-01 | £3.95 |
| 96 | Christopher Osborn | Unbound | | NOVEL | 9781911350071 | 2017-09-14 | 2017-09-14 | £14.99 |
| 97 | Sam Osman | Quicksilver | | NOVEL | 9781407105734 | 2010-01-04 | 2010-01-04 | £7.99 |
| 98 | Charlene Osmond | Creatures of the Night: A Beth Duncan Story | | NOVEL | 9781908268181 | 2011-09-01 | 2011-09-01 | £9.00 |
| 99 | J. D. Oswald | Dreamwalker | The Ballad of Sir Benfro | NOVEL | 9781405917728 | 2013-12-19 | 2013-12-19 | £4.99 |
| 100 | J. D. Oswald | The Broken World | The Ballad of Sir Benfro | NOVEL | 9781405917797 | 2015-09-24 | 2015-09-24 | £4.99 |
| 101 | J. D. Oswald | The Golden Cage | The Ballad of Sir Benfro | NOVEL | 9781405917742 | 2013-12-19 | 2013-12-19 | £4.99 |
| 102 | J. D. Oswald | The Obsidian Throne | The Ballad of Sir Benfro | NOVEL | 9781405917810 | 2016-09-22 | 2016-10-20 | £4.99 |
| 103 | J. D. Oswald | The Rose Cord | The Ballad of Sir Benfro | NOVEL | 9781405917704 | 2013-12-19 | 2013-12-19 | £4.99 |
| 104 | Shaun Othen | Excerpts from the Everyday Unknown | | NOVEL | 9780957043305 | 2011-09-26 | 2011-09-26 | £10.99 |
| 105 | Susan Oudot | Virtual Love | | NOVEL | 0671854704 | 1997-05-01 | 1998-02-01 | £5.99 |
| 106 | Chris Ould | Road Lines | | NOVEL | 0586070303 | 1985-07-01 | 1987-02-01 | £2.95 |
| 107 | Gillian Overitt | Max's Magical Dream | | NOVEL | 9781846247187 | 2012-06-28 | 2012-06-28 | £9.99 |
| 108 | David Owen | All the Lonely People | | NOVEL | 9780349003207 | 2019-01-10 | 2019-01-10 | £7.99 |
| 109 | David Owen | The Fallen Children | | NOVEL | 9780349002699 | 2017-05-04 | 2017-05-04 | £7.99 |
| 110 | Frank Owen (21st century) | South | | NOVEL | 9781782398929 | 2016-07-07 | 2017-03-02 | £7.99 |
| 111 | Stephen Owen | The Bloods of Space | | NOVEL | 9781906385309 | 2011-10-01 | 2011-10-01 | £8.45 |
| 112 | Thomas Owen | The House of Oracles and Other Stories | | COLLECTION | 9781905784493 | 2012-12-12 | 2012-12-12 | £35.00 |
| 113 | Gareth Owens | Fun with Rainbows | | COLLECTION | 9780956392404 | 2010-01-01 | 2010-01-20 | £7.99 |
| 114 | Kevin Oxland | The Cube of Asgard | Lost Souls (Oxland) | NOVEL | 9780957024205 | 2011-09-05 | 2011-09-05 | £8.99 |
| 115 | Dorothy Oxley | Quest | | NOVEL | 0745918468 | 1990-04-01 | 1990-01-01 | £2.25 |
| 116 | Sanem Ozdural | LiGa | LiGa Universe | NOVEL | 9781908168061 | 2012-07-31 | 2012-12-03 | £9.99 |
| 117 | Sanem Ozdural | The Dark Shall Do What Light Cannot | LiGa Universe | NOVEL | 9781908168641 | 2015-07-27 | 2015-07-27 | £9.99 |