How long will a 9V power a 12V fan?

[hansoloway]

Just like it says, I've got a 12V radioshack fan, the smallest available, and I was wondering for those with experience, how long will it last on one 9V battery?

 

[codyfett]

the nine volt in my freinds effects peadal ran for like three whole days he forgot to un plug it

 

[cal196]

I have a lithium rechargable battery and I stuck it to a mini fan and let it run just to see how long it would go, and it lasted about 8 hours.