To increase Magicka in The Elder Scrolls IV: Oblivion, you can use several methods:

Permanent Magicka Increase

• Raise Intelligence Attribute: The primary way to permanently increase your maximum Magicka is by increasing your Intelligence attribute when you level up

• Raise Willpower Attribute: This increases Magicka regeneration rate, which helps sustain Magicka over time

• Choose a Race with Magicka Bonuses: High Elves get +100 Magicka, and Bretons also have increased Magicka, making them ideal for spellcasters

• Select Birthsigns That Boost Magicka: The Atronach birthsign grants +150 Magicka, and the Mage or Apprentice birthsigns also increase Magicka

• Complete Quests and Use Items: Certain quests and items can increase Intelligence or Magicka, such as the Necromancer's Amulet (+158 Magicka), Scales of Pitiless Justice (+2 Intelligence), and the Birthright of Astalon (+50 Magicka)

Equipment and Enchantments

• Enchant Gear with Fortify Magicka: Use Transcendent Sigil Stones to enchant multiple pieces of gear (armor, rings, amulet) with +50 Magicka each. Wearing 7-9 such enchanted items can add hundreds of Magicka

• Use Rings and Amulets: Items like the Ring of Perfection and Necromancer's Amulet provide substantial Magicka boosts

Temporary Boosts and Potions

• Cast Fortify Magicka Spells: Temporary spells can boost Magicka for a limited time

• Use Potions: Potions of Fortify Magicka increase your Magicka pool temporarily

Advanced Techniques

• Magicka Glitches: There are known glitches involving casting specific spells (Fortify Attribute, Fortify Magicka, Drain Magicka) in sequence to gain effectively unlimited Magicka

. However, these are exploits rather than intended game mechanics.

Summary

• Focus on increasing Intelligence for maximum Magicka.
• Equip and enchant gear with Fortify Magicka effects.
• Choose races and birthsigns that boost Magicka.
• Raise Willpower to improve Magicka regeneration.
• Use potions and spells for temporary boosts.
• Optionally, use known glitches for infinite Magicka.

This combination can yield very high Magicka pools, with the highest legitimate builds reaching over 600 Magicka and beyond with enchantments and buffs