The Elder Scrolls 4: Oblivion features an interesting mechanic - the ability to become a vampire. This can be both a blessing and a curse for the main character. In this guide, we'll examine in detail how to transform into a bloodsucker or cure yourself of vampirism.
How to Become a Vampire
There are three major ways of vampirism. The simplest one is to acquire Porphyric Hemophilia during a fight with a vampire. After you've infected you with it, don't cure it for three days, then sleep. And then you'll wake up a first-stage vampire with appearance completely changed.

Cyrodiil is filled with areas populated with vampires: Barren Cave, Bloodcrust Cavern, Crowhaven, Fort Carmala, Fort Hastrel, Fort Redman, Gutted Mine, Lipsand Tarn, Memorial Cave, Redwater Slough, and many others. Even if you've already visited an area, you can return after enemy respawn for a repeat battle with bloodsuckers.

The second one is the Dark Brotherhood. After completing all the quests for Vicente Valtieri, choose the "Dark Gift" option when speaking to him. This starts the "Darkness Eternal" quest. Sleep, and Vicente will come over and bite you. You wake up infected with Porphyric Hemophilia, and then you will have to wait three days in order to fully become it.
The third choice is available in the Mehrunes Razor DLC. Acquire the Beating Heart from Msirae Faythung during the Unearthing Mehrunes Razor quest. The heart may be eaten to infect or cooked into a potion with complete alchemy skill. Either of these requires a three-day wait.
Vampire Stages and Their Features
Vampirism is in stages of 25%, 50%, 75%, and 100%. With each stage, the character's appearance degenerates - they get increasingly old, eyes turn pinkish-red, facial hair loses all its follicles, and skin alters color completely.

The sun becomes the vampire's nemesis. After you've progressed beyond 25%, sunlight will harm you - most at noon, least during dawn and sunset. You can't wait or fast travel during sunlight. To remain at the first level, you need to feed every 24 hours.

To murder, spot a sleeping victim, go near them silently, and use the interaction key. This is not a murder but a crime if detected. Make sure there are no guards nearby. Homeless victims, not in secure houses, can be devoured.

Vampire Abilities
After completing all four stages, the vampires receive access to special abilities. Hunter's Sight gives 30 seconds of night vision and detection of life at a distance of up to 100 feet and uses 5 magicka points but can be used an infinite amount of times.

Vampire's Seduction lures a human upon touch for 50 points for 20 seconds but once a day. Reign of Terror creates a silence area up to 20 feet for 60 seconds and demoralizes up to level 6 monsters upon touch, used once a day.
Embrace of Shadows is the strongest power, giving night vision for 90 seconds and camouflage for 180 seconds. Available once a day and priceless for sneaky movement.
Curing Vampirism
If vampirism is not your cup of tea, there is a cure for it. Prior to complete transformation (within 72 hours of the infection), a cure disease potion, "Cure Disease" spell, mandrake root, shepherd's pie, or praying at a shrine will resolve the problem.
When converted, you will need to complete the very long "Vampire Cure" quest line. Start with Raminus Polus at the Arcane University in the south part of the Imperial City. He'll direct you to the Count of Skingrad, who will direct you to Melisande - a witch who lives in a cabin to the east of the Imperial City.

Melisande will offer her assistance for a fee: five vacant Grand Soul Gems. These exist in various dungeons or can be purchased at Mages Guilds for 300-350 gold apiece. Once Melisande receives the gems, she will give the ingredients to create the healing potion.

Ingredients for the Healing Potion
There are five ingredients that need to be added to the potion. Bloodgrass is easily found at Oblivion gates, where it grows abundantly. Garlic is sold by merchants in Skingrad.

Nightshade is rarer, but there's plenty south of Skingrad. Search for a large rock about halfway between the city and the map edge, with nightshade growths surrounding it. The rock is atop a hill roughly fifty yards south of the Fat Ramp camp.
To obtain Argonian blood, Melisande will give you an enchanted dagger. Go to the Waterfront district of the Imperial City, find an Argonian behind the shacks, raise their disposition, and stab them with the dagger. They will neither resist nor call guards. Another alternative is Veyond Cave north of Bruma, which is infested with hostile Argonian tribes.

The final ingredient is the ashes of a specific vampire, Hindaril, from Redwater Slough location, which will be marked on your map by Melisande. There are some vampires in the cave, but Hindaril is the strongest. He is a hand-to-hand combatant and has the ability to take weapons from dead friends, so be prepared for a long battle.
Completing the Cure
After you acquire all the ingredients, give them to Melisande and let it prepare for 24 hours. She will provide you with two doses, one for you and another for Count Hassildor's wife. Return to Skingrad to Hal-Liurz in the castle county hall. She will lead you through a secret tunnel to the count and his wife.

Give the cure to the count for his wife and witness the mournful death of the countess's disease. The count will ask for time to consider. Leave the tunnel, wait for 24 hours, and then speak with Hal-Liurz once more. The count will thank you for your help and give you gold as reward, completing the quest.

Fact to remember: after vampirism has been cured, repeated transformation is not possible. So, balance carefully all pros and cons before coming to a final decision.
Vampirism in Oblivion Remastered FAQ
Q1: How do you become a vampire in The Elder Scrolls 4: Oblivion? There are three ways to become a vampire in Oblivion. First, get infected with Porphyric Hemophilia during combat with vampires in locations like Barren Cave, Bloodcrust Cavern, Crowhaven, Fort Carmala, Fort Hastrel, Fort Redman, Gutted Mine, Lipsand Tarn, Memorial Cave, or Redwater Slough. Don't cure the disease for three days, then sleep to transform. Second, complete Dark Brotherhood quests for Vicente Valtieri and choose the "Dark Gift" option to start "Darkness Eternal" quest. Third, in Mehrunes Razor DLC, obtain the Beating Heart from Msirae Faythung during Unearthing Mehrunes Razor quest.
Q2: What are the vampire stages and their features in Oblivion? Vampirism has four stages: 25%, 50%, 75%, and 100%. Each vampire stage changes your character's appearance - eyes turn pinkish-red, facial hair disappears, skin color alters, and you look increasingly old. Sunlight becomes harmful after 25% stage, with most damage at noon and least during dawn and sunset. You cannot wait or fast travel during sunlight. To remain at first level, feed every 24 hours on sleeping victims.
Q3: What vampire abilities do you get in Oblivion? Vampires receive special abilities after completing all four stages. Hunter's Sight provides 30 seconds of night vision and life detection up to 100 feet, using 5 magicka points with unlimited uses. Vampire's Seduction charms humans for 50 points for 20 seconds, once daily. Reign of Terror creates silence area up to 20 feet for 60 seconds and demoralizes level 6 monsters, once daily. Embrace of Shadows gives night vision for 90 seconds and camouflage for 180 seconds, once daily.
Q4: How do you cure vampirism in Oblivion? Before complete transformation (within 72 hours of Porphyric Hemophilia infection), use cure disease potion, "Cure Disease" spell, mandrake root, shepherd's pie, or pray at shrine. After transformation, complete the "Vampire Cure" questline. Start with Raminus Polus at Arcane University in Imperial City, who directs you to Count of Skingrad, then to Melisande witch east of Imperial City.
Q5: What ingredients are needed for the vampire cure healing potion? Five ingredients are required: Bloodgrass (found at Oblivion gates), Garlic (sold by Skingrad merchants), Nightshade (south of Skingrad near large rock), Argonian blood (obtained with enchanted dagger from Melisande at Waterfront district or Veyond Cave north of Bruma), and ashes of vampire Hindaril from Redwater Slough location.
Q6: How much do Grand Soul Gems cost for the vampire cure? Melisande requires five vacant Grand Soul Gems as payment for vampire cure assistance. These gems cost 300-350 gold each at Mages Guilds or can be found in various dungeons throughout Cyrodiil.
Q7: Where can you find vampires to get infected in Oblivion? Vampires populate many areas in Cyrodiil including Barren Cave, Bloodcrust Cavern, Crowhaven, Fort Carmala, Fort Hastrel, Fort Redman, Gutted Mine, Lipsand Tarn, Memorial Cave, Redwater Slough, and many other locations. You can return to previously visited areas after enemy respawn for repeat battles with bloodsuckers.
Q8: Can you become a vampire again after being cured in Oblivion? No, after vampirism has been cured in Oblivion, repeated transformation is not possible. This is permanent, so carefully balance all pros and cons of vampire abilities versus sunlight weakness before making your final decision to cure vampirism.
Q9: How do you feed as a vampire in Oblivion? To feed as vampire, find sleeping victims and approach them silently. Use interaction key near sleeping NPCs. Feeding is considered crime if detected by guards, so ensure no witnesses nearby. Homeless victims not in secure houses can be fed upon safely.
Q10: What happens during the final vampire cure quest completion? After obtaining all healing potion ingredients, give them to Melisande and wait 24 hours. She provides two doses - one for you and another for Count Hassildor's wife. Return to Skingrad castle, meet Hal-Liurz who leads you through secret tunnel to count and his wife. Give cure to count for his wife, witness countess's cure, wait 24 hours, then receive gold reward from grateful count.