Open Wounds

% Chance of Open Wounds can cause target to bleed uncontrollably when applied with a successful weapon attack, draining life and stopping any unit damage regeneration for its 8 second (200 frame) duration. Bleeding occurs even when life drain cannot be applied to target.
% Chance from multiple sources is summed, although when two weapons are equipped only that of the attacking weapon is added (that of the other weapon is ignored). >100% Chance is redundant.
Applied by any melee or ranged attack with the exception of Blade Sentinel, Blade Shield and the additional arrows of Multiple Shot (only applied by the original two arrows).
Always applied to another player, but only applied to other units (monster, hireling or pet) if their life value changes, either due to damage taken or regenerated. If no damage is taken then OW won't be applied if regeneration has already been stopped by Prevent Monster Heal.
Life drain is dependent on the level of the player, hireling or Iron Golem applying it. Life drain per frame in bits (1 bit = 1/256 point) is currently calculated as follows:

Stat	Level
Stat	1-15	16-30	31-45	46-60	>60
Bit Life Drain/Frame	(9*lvl)+31	(18*lvl)-104	(27*lvl)-374	(36*lvl)-779	(45*lvl)-1319

[1] [2]

Life drain per frame in bits may then be modified depending on the attack used and the target, and rounded down to the nearest bit:

Target	Modifier
Special Unit (Any Attack)	/2
Player (Melee Attack)	/4
Player (Ranged Attack)	/8

[3]

Special units are monsters other than normal and minion monsters (Champion, Unique, Super Unique, boss (excluding normal and minion Putrid Defilers) and Prime Evil). Life drain is unmodified against all other targets.
Although duration is 8 seconds (200 frames), life drain is not applied in the first frame and so points of life drain are calculated as follows:

Life Drain	Multiplier
Points/Second	*25/256
Total Points	*199/256

Life drain cannot be countered by any form of damage reduction.
Duration cannot be reduced by Cleansing or Fade. [4] [5]
When OW is applied again before the previous duration expires, duration simply gets reset regardless of the level of the second application: if OW is applied at level 80 while it is still being applied at level 60, level 60 damage is still applied for the reset duration (and vice versa).
Poison damage and length can be applied separately and simultaneously. [6]
Replenish Life and + Life After Each (Demon) Kill from items, and healing from potions, Prayer (including its passive bonuses to Cleansing and Meditation) and Holy Bolt still apply while active.
Replenish Life from items is a direct counter: OW applied by a level 30 player's melee attack on another player would result in 109 bit life drain per frame, which Replenish Life +109 would counter entirely; a ranged attack would result in 54 bit life drain per frame, which Replenish Life +54 would counter entirely.

Source

Pelt

Template:D2 Skill bonus |- |33% !align=left|[[D2 Unique Druid pelt#Cerebus' Bite|Template:D2 Unique]] |71 !Yes |}

Body armor

Template:D2 Skill bonus |- |25% !align=left|[[D2 Unique Normal body armor#Boneflesh|Template:D2 Unique]] |35||No |- |33% |align=left|[[D2 Rune Word body armor#Duress|Template:D2 Unique bold]] body armor |47||No |- |35% !align=left|[[D2 Unique Exceptional body armor#Crow Caw|Template:D2 Unique]] |45||No |- |40% !align=left|[[D2 Unique Exceptional body armor#Toothrow|Template:D2 Unique]] |56||No |}

Weapon

Template:D2 Skill bonus |- |25% |align=left|[[D2 Rune|Template:D2 Crafted]] in weapon |47||No |}

Melee weapon

Template:D2 Skill bonus |- |66% |align=left|[[D2 Rune Word weapon#Fury|Template:D2 Unique bold]] melee weapon |65||No |- |100% |align=left|[[D2 Rune Word weapon#Malice|Template:D2 Unique bold]] melee weapon |15||No |}

Missile weapon

Template:D2 Skill bonus |- |30% !align=left|[[D2 Unique Exceptional bow#Riphook|Template:D2 Unique]] |39||No |- |33% !align=left|[[D2 Unique Exceptional crossbow#Langer Briser|Template:D2 Unique]] |40||No |- |33% !align=left|[[D2 Unique Elite crossbow#Gut Siphon|Template:D2 Unique]] |79||No |}

Axe

Template:D2 Skill bonus |- |15% !align=left|[[D2 Unique Normal axe#Skull Splitter|Template:D2 Unique]] |28||No |- |25% |align=left|[[D2 Rune Word blade#Crescent Moon|Template:D2 Unique bold]] axe |47||No |- |25% !align=left|[[D2 Unique Exceptional axe#Butcher's Pupil|Template:D2 Unique]] |47||No |- |25% |align=left|[[D2 Rune Word blade#Beast|Template:D2 Unique bold]] axe |63||No |- |25% |align=left|[[D2 Rune Word blade#Doom|Template:D2 Unique bold]] axe |67||No |- |33% !align=left|[[D2 Unique Exceptional throwing weapon#The Scalper|Template:D2 Unique]] |65||No |- |33% !align=left|[[D2 Unique Elite throwing weapon#Lacerator|Template:D2 Unique]] |76||No |- |50% !align=left|[[D2 Unique Normal axe#The Gnasher|Template:D2 Unique]] |7||No |- |50% |align=left|[[D2 Rune Word blade#Steel|Template:D2 Unique bold]] axe |13||No |- |50% |align=left|[[D2 Rune Word blade#Kingslayer|Template:D2 Unique bold]] axe |53||No |- |50% !align=left|[[D2 Unique Elite axe#Razor's Edge|Template:D2 Unique]] |75||No |- |60% !align=left|[[D2 Unique Normal axe#Goreshovel|Template:D2 Unique]] |19||No |}

Claw

Template:D2 Skill bonus |- |25% |align=left|[[D2 Rune Word blade#Chaos|Template:D2 Unique bold]] claw |57||No |}

Club

Template:D2 Skill bonus |- |25% !align=left|[[D2 Unique Exceptional club#Fleshrender|Template:D2 Unique]] |46||No |}

Dagger

Template:D2 Skill bonus |- |50% !align=left|[[D2 Unique Elite dagger|Template:D2 Unique]] |76||No |}

Hammer

Template:D2 Skill bonus |- |25% |align=left|[[D2 Rune Word blunt#Beast|Template:D2 Unique bold]] hammer |63||No |- |25% |align=left|[[D2 Rune Word blade#Doom|Template:D2 Unique bold]] hammer |67||No |}

Mace

Template:D2 Skill bonus |- |25% !align=left|[[D2 Unique Normal mace#Bloodrise|Template:D2 Unique]] |20||No |- |50% |align=left|[[D2 Rune Word blade#Steel|Template:D2 Unique bold]] mace |13||No |}

Polearm

Template:D2 Skill bonus |- |25% |align=left|[[D2 Rune Word blade#Crescent Moon|Template:D2 Unique bold]] polearm |47||No |- |25% |align=left|[[D2 Rune Word blade#Doom|Template:D2 Unique bold]] polearm |67||No |- |30% !align=left|[[D2 Unique Normal polearm#Soul Harvest|Template:D2 Unique]] |26||No |- |50% !align=left|[[D2 Unique Normal polearm#Woestave|Template:D2 Unique]] |38||No |- |50% !align=left|[[D2 Unique Exceptional polearm#The Meat Scraper|Template:D2 Unique]] |49||No |}

Scepter

Template:D2 Skill bonus |- |25% |align=left|[[D2 Rune Word blunt#Beast|Template:D2 Unique bold]] scepter |63||No |}

Spear

Template:D2 Skill bonus |- |35% !align=left|[[D2 Unique Normal spear#Bloodthief|Template:D2 Unique]] |23||No |- |40% !align=left|[[D2 Unique Exceptional spear#The Impaler|Template:D2 Unique]] |39||No |}

Sword

Template:D2 Skill bonus |- |25% |align=left|[[D2 Rune Word blade#Crescent Moon|Template:D2 Unique bold]] sword |47||No |- |33% !align=left|[[D2 Unique Normal sword#Blood Crescent|Template:D2 Unique]] |10||No |- |50% |align=left|[[D2 Rune Word blade#Steel|Template:D2 Unique bold]] sword |13||No |- |50% |align=left|[[D2 Rune Word blade#Kingslayer|Template:D2 Unique bold]] sword |53||No |- |50% !align=left|[[D2 Unique Elite sword#Bloodmoon|Template:D2 Unique]] |69||No |- |80% !align=left|[[D2 Unique Normal sword#Ripsaw|Template:D2 Unique]] |35||No |}

Throwing weapon

Template:D2 Skill bonus |- |33% !align=left|[[D2 Unique Exceptional throwing weapon#The Scalper|Template:D2 Unique]] |65||No |- |33% !align=left|[[D2 Unique Elite throwing weapon#Lacerator|Template:D2 Unique]] |76||No |}

Shield

Template:D2 Skill bonus |- |50% !align=left|[[D2 Unique Normal shield#Swordback Hold|Template:D2 Unique]] |20||No |}

Belt

Template:D2 Skill bonus |- |(5-10)% !align=left|[[D2 Crafted item#Blood|Template:D2 Crafted]] |13||No |}

Boots

Template:D2 Skill bonus |- |10% !align=left|[[D2 Unique Exceptional boots#Gorerider|Template:D2 Unique]] |55||No |}

Gloves

Template:D2 Skill bonus |- |25% !align=left|[[D2 Unique Elite gloves#Dracul's Grasp|Template:D2 Unique]] |84||No |}

Set bonus

Template:D2 Skill bonus |- |20% |align=left|[[D2 Infernal Tools|Template:D2 Set bold]] (Full) |5||No |}

References

Special Magic Effects (Arreat Summit)
Open Wounds (Technical Discussion)
Nefarius, Open Wounds Explained (v1.11b) (Phrozen Keep)