The only reason that it sometimes doesn't pay to buy in bulk is if the oil you're using gets superceded by a new evolution in oil. In the (relatively) short time I've been here ..there have been major creations and extinctions of oils ..and I've got about two or three years (if I go like I should) of "oil reserve". If some new "Holy Grail" comes out and proves to be the hot setup ..my reserve just got depreicated to junk.
Since I've been here (in no particular order):
Mobil came out with a line of 0w-X oils
Mobil eliminated some of the 0w-x oils
Mobil came out with "R"
Mobil "R" can't be found
MC 5w-20 came out.
GC came out ..or was at least I became aware of it
Mobil EP oils debute
Mobil 1 Truck and SUV came out
We've gone from SL to SM (it may have been SJ when I joined
)
G4 and a variety of other evolutions occured
I've seen MB 229.X been expounded upon for mulitiple threads ...and then had a new focus upon VW 505.X
I could go on. This is sorta like the upramp in cpu speeds. Today's hot setup is tomorrow's old news.
So unless your fleet is going to remain stable for the next year ..and you can realize no advantages in improvements in oil formulations, it doesn't really pay to keep too much of an inventory.