For those of you who do your own oil changes, how do you buy engine oil? How do you get good deals on it? Yes, there are always a few good deals around but the problem is there are SO MANY grades / specs of oil that the chances your exact spec is on special is rare.
For example, one of my cars requires 10W-30, API grade SL "Energy-Conserving", SM "Energy-Conserving", SN "Resource-Conserving" or ILSAC multigrade engine oil. It's hard enough finding that amongst the 100s of other oils on the shelves, let alone finding one on special.
Associated question - Is it bad if I don't exactly follow the spec, eg I get a 5W-30, SP or whatever?
All of the big auto parts suppliers allow you to enter your car registration to identify it. Double check it selects the correct model/engine option etc.
From there you can shop only for parts that suit your vehicle. Filter down the parts selection to oil and a list of suitable oils will be presented.
See which one is on special and compare to other outlets to double check it's a deal.
LPT: buy it when it's on special not when you need it. Oil stores well in the garage. The week you need it you can guarantee there's none on special.