Is there any definite number of how many dungeons you can crawl through in oblivion?
I apologize if this has been asked before as I didn't find anything with the search function nor google.

lots.

Well I was more looking for a number...

To be more precise, I think it's somewhere between "lots" and "a hell of a lot".

:P

Okay, okay. You can count how many there are http://www.uesp.net/wiki/Oblivion:Forts, http://www.uesp.net/wiki/Oblivion:Ayleid_Ruins, http://www.uesp.net/wiki/Oblivion:Mines and http://www.uesp.net/wiki/Oblivion:Caves, and add those together, if you really need an exact number. I couldn't find any sources stating the exact number of dungeons (and it sorta depends on what you count as a "dungeon", I included mines, forts, ruins and caves in the above links).

All right I counted 221 (54+52+24+91)
Thanks!

And the other answer is five. Caves and mines are one (the mines just add a few things like veins of ore), Fort ruins are the second, Ayleid ruins the third, and Oblivion tunnels the fourth, Sewers the fifth if you go by architecture.

Or maybe it's nine, Marauder, Bandit, Undead, Vampire, Creature, Goblin, Daedra, Conjurer and Necromancer if you go by who you meet.

Even multiplying those together you'll find a bit of deja vu when it's Necromancers in an Ayleid ruin again. And an Oblivion Tunnel will only have Daedra in it, so it's really less than that. You do find a few dungeons that have sections of more than one architecture, and more than one enemy type, sometimes even in conflict with each other, but there are finite choices to work with, and a fair amount of duplication is inevitable. On the other hand, the same dungeon can have a different selection of enemies if you go back later after leveling up, as creatures and undead come from leveled lists that provide a different result at a different level. The human enemies will get changed equipment the same way.

Have we destroyed the original question enough yet?

221 dungeons that are actually five.

At least there are a few unique dungeons. I remember sideways cave for example.

There are LOTS but they are dumb because all of the loot is randomized.

SPOILER:
http://www.uesp.net/wiki/Oblivion:Rockmilk_Cave