| Publication | Code | Date | Publisher | System (Setting) |
|---|
 O Brave New World | | 2014 | Self Published | Lamentations of the Flame Princess
|
| Obelisk: The Howling | | 2011 | Self Published | Risus
|
| Objective Zebra | | 2011 | Bully Pulpit Games | Fiasco Classic
|
 The Obligatory Cthulhu Set | AEG 5503 | 2013 | Alderac Entertainment Group | Smash Up
|
 Observer Effect | APU8109 | 2017 | Arc Dream Publishing | Delta Green
|
 Occult Odds and Ends | | n/a | Self Published | Call of Cthulhu (Classic)
|
| Octomaid Promo Card | | Jun 2016 | Steve Jackson Games | Munchkin
|
| Of Keys and Gates | PAG2101 | 1995 | Pagan Publishing | Call of Cthulhu (Classic)
|
| Of Sound Mind and Body | | 2001 | Self Published | Call of Cthulhu (Gaslight)
|
| Of Wrath and Blood * | | Apr 2019 | Chaosium | Call of Cthulhu (Classic)
|
| Old Blood | | 1996 | Self Published | Call of Cthulhu (Now)
|
| The Old Man of Damascus * | SKP0701 | 2007 | Skirmisher Publishing | Call of Cthulhu (Classic)
|
| Old Man Tompkins | | Jun 2019 | Chaosium | Call of Cthulhu (Classic)
|
| Old One | | 2020 | Grimlord Games | The Everrain
|
| Old Ones | | 2016 | Epic Level NPC | Pathfinder
|
 Old Ones Rising * | | 2017 | Arc Dream Publishing | |
| The Oldskull Necronomicon | LOV1 | 2017 | Wonderland Imprints | Advanced Dungeons and Dragons
|
| Oliver Grayson * | | 2011 | Fantasy Flight Games | Arkham Horror
|
| Omega Master Rulebook | CW-E12 | 2017 | Petersen Games | Cthulhu Wars
|
| Omens of Ice | SL17 | 2016 | Fantasy Flight Games | Elder Sign
|
| Omens of the Deep | SL19 | 2017 | Fantasy Flight Games | Elder Sign
|
| Omens of the Pharaoh | SL20 | 2018 | Fantasy Flight Games | Elder Sign
|
 Omniverse | 1 | 1984 | Quartzlords | Call of Cthulhu (Classic)
|
| On a Wing and a Wave | | 2011 | Drakat Games | Call of Cthulhu (Classic)
|
| On the Banks of the Ohio | | 2019 | Chaosium | Call of Cthulhu (Classic)
|
| On the Fringes | | 2013 | Reality Blurs | tremulus
|
| The Once and Future King | | 1999 | Self Published | Call of Cthulhu (Classic)
|
| Once in a Lifetime | 1 | 1986 | Self Published | Call of Cthulhu (Classic)
|
| Once Men | CHA0356 | 2008 | Chaosium | Call of Cthulhu (Once Men)
|
| One for the Money | PELGOC04D | 2017 | Pelgrane Press | Gumshoe (Cthulhu Confidential)
|
| One Friday Night | | Aug 2020 | Chaosium | Call of Cthulhu (Now)
|
| One Less Grave | | Nov 2020 | Chaosium | Call of Cthulhu (Classic)
|
| One of Us | | 2008 | Self Published | Call of Cthulhu (Classic)
|
| One of Us Becomes and Evil God! | | 2017 | AHC | One of Us Becomes and Evil God!
|
| One Page Sanity Loss | | Apr 2020 | Chaosium | Call of Cthulhu (Classic)
|
| One Starry Night | | 2018 | Skirmisher Publishing | Call of Cthulhu (Classic)
|
 One Thousand and One Nights and One Night | 26 | Mar 2008 | Self Published | Call of Cthulhu (Classic)
, Call of Cthulhu (WWI)
|
| One Thousand and One Nights and One Night | 32 | Jun 2008 | Self Published | Call of Cthulhu (WWI)
|
| An Oneiric Resistance | | 2016 | Xipe Totec Press | |
| Onslaught 3 Stretch Goal Box | CW-E20 | 2019 | Petersen Games | Cthulhu Wars
|
| Opener of the Way | CW-F1 | 2015 | Petersen Games | Cthulhu Wars
|
| Operation DUSTBOWL | | 2017 | Self Published | Call of Cthulhu (Delta Green)
|
| Operation Foxglove | | Aug 2021 | Chaosium | Call of Cthulhu (WWII)
|
| Operation Hope | | Mar 2020 | Chaosium | Call of Cthulhu (Strange Aeons: The Reaping)
|
| Operation Vanguard | MUH052302 | 2021 | Modiphius Entertainment | |
| Opifex Bimonthly | 1 | 1996 | Self Published | Call of Cthulhu (Classic)
, Call of Cthulhu (Now)
|
| Opifex Bimonthly | 2 | 1996 | Self Published | Call of Cthulhu (Classic)
|
| Opifex Bimonthly | 3 | 1996 | Self Published | Call of Cthulhu (Now)
|
| Opifex Bimonthly | 4 | 1996 | Self Published | Call of Cthulhu (Now)
|
| Opifex Bimonthly | 5 | 1996 | Self Published | Call of Cthulhu (Now)
|
| Opifex Bimonthly | 6 | Mar 1997 | Self Published | Call of Cthulhu (Now)
|
| Opifex Bimonthly | 7 | May 1997 | Self Published | Call of Cthulhu (Classic)
, Call of Cthulhu (Now)
|
| Opifex Bimonthly | 8 | Jul 1997 | Self Published | Call of Cthulhu (Classic)
, Call of Cthulhu (Now)
|
| Opifex Bimonthly | 9 | Sep 1997 | Self Published | Call of Cthulhu (Classic)
|
| Opifex Bimonthly | 11 | Jan 1998 | Self Published | Call of Cthulhu (Classic)
, Call of Cthulhu (Now)
|
| Opifex Bimonthly | 12 | Mar 1998 | Self Published | Call of Cthulhu (Classic)
, Call of Cthulhu (Now)
|
| Opifex Bimonthly | 13 | May 1998 | Self Published | Call of Cthulhu (Now)
|
| Opifex Bimonthly | 14 | Jul 1998 | Self Published | Call of Cthulhu (Now)
|
| Opifex Bimonthly | 15 | Sep 1998 | Self Published | Call of Cthulhu (Now)
|
| Opifex Bimonthly | 16 | Nov 1998 | Self Published | Call of Cthulhu (Classic)
, Call of Cthulhu (Delta Green)
, Call of Cthulhu (Now)
|
| Opifex Bimonthly | 17 | Jan 1999 | Self Published | Call of Cthulhu (Now)
|
| Opifex Bimonthly | 18 | Mar 1999 | Self Published | Call of Cthulhu (Classic)
|
| Opifex Bimonthly | 19 | May 1999 | Self Published | Call of Cthulhu (Classic)
, Call of Cthulhu (Now)
|
| Opifex Bimonthly | 20 | Jul 1999 | Self Published | Call of Cthulhu (Classic)
|
| Opifex Bimonthly | 21 | Sep 1999 | Self Published | Call of Cthulhu (Classic)
|
| Opifex Bimonthly | 22 | Nov 1999 | Self Published | Call of Cthulhu (Gaslight)
, Call of Cthulhu (Now)
|
| Opifex Bimonthly | 23 | Jan 2000 | Self Published | Call of Cthulhu (Now)
|
| Opifex Bimonthly | 24 | Mar 2000 | Self Published | Call of Cthulhu (Now)
|
 The Order of the Silver Twilight | CT33 | 2010 | Fantasy Flight Games | Call of Cthulhu LCG
|
| Orient Express Tickets | | Sep 2018 | Chaosium | Call of Cthulhu (Classic)
|
| Orphan School Horror | cr3005i | 2017 | Cthulhu Reborn | Call of Cthulhu (Convicts)
|
| The Orphanage | | Dec 2019 | Chaosium | Call of Cthulhu (Classic)
|
| The Other Side | | 2012 | Fainting Goat Games | ICONS
|
| The Other Side of the Mirror | SG-MT4 | 2012 | Spectrum Games | Macabre Tales
|
| Our Ladies of Sorrow | MRP0005 | 2009 | Miskatonic River Press | Call of Cthulhu (Now)
|
| Out of Space | PELGT30 | 2013 | Pelgrane Press | Trail of Cthulhu
|
| Out of the Depths | | 1992 | Self Published | Call of Cthulhu (Now)
|
| Out of the Past | | May 2019 | Chaosium | Call of Cthulhu (Classic)
|
| Out of the Vault | PAG1009 | 2002 | Pagan Publishing | Call of Cthulhu (Classic)
|
| Out of the Woods | PELGT43 | 2017 | Pelgrane Press | Trail of Cthulhu
|
| Out of Time | PELGT22 | 2011 | Pelgrane Press | Trail of Cthulhu
|
| The Outer Presence | | 2015 | Kort'thalis Publishing | The Outer Presence
|
| The Outpost of the Outer Ones | YS1 | 2015 | Self Published | Advanced Dungeons and Dragons
|
| Overkill: Investigator Weapons Volume 2.1 * | 60-IHB02.1-P | 2020 | Sixtystone Press | Call of Cthulhu (Now)
|
 Oversized 3-5 Player Earth Map | CW-M13 | 2018 | Petersen Games | Cthulhu Wars
|
| The Oxford Articles | | Aug 2021 | Chaosium | Call of Cthulhu (Strange Aeons: 1953)
|