Probably stackable with this Valvoline rebate for $10 off 5 quarts of Valvoline, bringing cost down to $0.88 / qt. + pre-rebates sales tax.
Form on Team Valvoline site says any 5 quarts, so loose quarts ought to qualify just as well as 5 quart jugs.
“He who does not value the teacher, Or greatly care for the material, Is greatly deluded although he may be learned." - Lao-Tzu