- Objective Five (2000)[6] 1-6
- Oblivion Song (2018)[1] 1
- Ocean (2004)[6] 1-6
- The October Faction (2014)[18] 1-18
- The Official Handbook of the Marvel Universe: Master Edition (1990)[36] 1-36
- Oh, Hell (2016)[2] 1-2
- Oh My Goddess!: Part III (1995)[11] 1-11
- Oh My Goddess!: Part VIII (2000)[6] 1-6
- Old Man Logan (2015)[5] 1-5
- Old Man Logan (2016)[35] 1-17,21,23-39
- Old World 50 (2017)[1] 0
- Oliver & Columbine (2006)[12] 1-12
- Olympus Heights (2004)[5] 1-5
- O.M.A.C. (2011)[7] 2-8
- The OMAC Project (2005)[6] 1-6
- Omega Chase (2007)[5] 1-5
- The Omega Men (1983)[38] 1-38
- The Omega Men (2015)[12] 1-12
- Once Our Land (2016)[1] 2
- One for One: Star Wars (2013)[1] 1
- One Plus One (2002)[5] 1-5
- Oni (2001)[4] 0-3
- The Only Living Boy (2012)[2] 1-2
- Optimus Prime (2016)[12] 1-5,7,11-14,16,18
- Optimus Prime: First Strike (2017)[1] 1
- The Order of the Stick (2005)[6] 0-5
- The Original Ghost Rider Rides Again (1991)[7] 1-7
- Orion (2000)[25] 1-25
- Orphan Black: Deviations (2017)[6] 1-6
- Orphan Black: Helsinki (2015)[5] 1-5
- The Other Dead (2013)[6] 1-6
- Our Army at War (1952)[301] 1-301
- Outcast by Kirkman & Azaceta (2014)[23] 1-13,25-34
- Out For Blood (1999)[4] 1-4
- Outlanders (1988)[34] 0-33
- Outlaw Nation (2000)[19] 1-19
- The Outlaws (1952)[5] 10-14
- Out Of The Night (1952)[17] 1-17
- Out of the Vortex (1993)[12] 1-12
- Overrun (2016)[4] 1-4
- Over the Garden Wall (2016)[18] 1-8,10-19
- Overwatch (2016)[13] 1-13
