So, i actually went to amazon and took a look. Looking only at 5W-30 since that's what the wrx and outback take.
There are 5:
21.16 = 1.76/qt

- ACDelco 19287565 Mobil 1 5W-30 ESP Formula Engine Oil - 1 Quart, (Pack of 12)
19.48 = 3.25/qt - ACDelco 19287564 Mobil 1 5W-30 EP Engine Oil - 1 Quart, (Pack of 6)
18.61 = 3.10/qt - ACDelco 19287554 Mobil 1 5W-30 Engine Oil - 1 Quart, (Pack of 6)
31.48 = 7.87/qt - ACDelco 19210933 Mobil 1 5W-30 Synthetic Engine Oil - 1 Gallon
34.65 = ????.qt - ACDelco 19287557 Mobil 1 5W-30 Engine Oil
In this format, it's easy to see the diffs between them.
According to Mobil, all "Mobil 1" is synthetic oil.
EP is "Extended Performance", comes with a gold label.
ESP is "Emission System Protection", green label (duh).
I did some googling of the part #s - included in the product description - and the only real hits were nextag and shopzilla - shopping comparison sites and the only hits they returned were essentially the same amazon pages I started from.
So, what did I do? While on Mobil's site, I checked their FAQ on shelf-life - 5 years sealed, stored cool & dry. I bought a lot of the ESP. I'll resell it if I don't use it.
It's not really taking a chance either. If it's not Mobil 1, but simply Mobil Super, you complain to Amazon and they'll almost certainly refund your money and most likely, will allow you to keep the oil. I've had a dozen claims this year and every one was decided in my favor within hours and I haven't had to return a single item - they're almost falling over themselves to thank you for finding the problem and allowing them to fix it for you.
And if they cancel the order(s), no loss other than the time and heck, at this price, it's a better chance than a lottery ticket!
