There are 100 possible locations where Oblivion Gates can appear in The Elder Scrolls IV: Oblivion, but during a single playthrough, no more than 60 gates will actually open. This includes 20 fixed gates that always open at specific points in the main quest, and up to 40 additional gates that spawn randomly from a pool of 80 possible random locations. Once a gate is closed, it will not reopen without using console commands

. Specifically:

• 20 fixed gates always open during the main quest, including 10 gates that appear after the quest "Find the Heir" which lead to specific Oblivion worlds.
• Up to 40 random gates can open from 80 possible random locations, but the total number of gates open at any one time will never exceed 60.
• The first gate appears at Kvatch at the start of the game.
• Completing the main quest closes all gates permanently and prevents new ones from opening

In summary, while there are 100 potential gate locations, the maximum number of Oblivion Gates that can appear and be closed in one playthrough is 60.