The Elder Scrolls IV: Oblivion has approximately the following number of quests:

• The original base game contains 223 quests (213 with journal entries and 10 without).
• The official smaller downloadable content (DLC), including Knights of the Nine, adds 19 quests (18 with journal entries and 1 without).
• The Shivering Isles expansion adds 35 quests (33 with journal entries and 2 without).

In total, including the base game and all official DLCs, there are about 277 quests

. A single character can complete up to around 248 to 251 quests in one playthrough due to some quests conflicting or competing with one another

. Breaking down the quests by type and content:

• Main Quest: 18 quests
• Fighters Guild: 20 quests
• Mages Guild: 18 quests
• Thieves Guild: 13 quests
• Dark Brotherhood: 20 quests
• Arena: 2 quests
• Daedric Quests: 15 quests
• Master Trainer Quests: 21 quests
• Various city and settlement quests add up to many more side quests
• Knights of the Nine DLC: 11 quests
• Shivering Isles expansion: 35 quests

Therefore, the total number of quests in Oblivion, including all DLCs, is roughly 277 quests, with some variation depending on how quests are counted and journal entries considered