Costco currently has the 6 quart packs of Mobil 1 marked down $10, this can be combined with the current Mobil 1 rebate of $12 and get you 6 quarts at $2.78/quart. While this is a bit more per quart than buying jugs its still a great deal for people who prefer individual quarts over jugs.
Costco discount valid 4/15-4/28.
$38.69 per 6qt pack
-$10 Costco discount
-$12 Mobil 1 rebate
= $16.69 or $2.78 per quart
Limit of 5 per household
Full Synthetic 5W-30
Full Synthetic 5W-20
Full Synthetic 10W-30
Full Synthetic 0W-40
Advanced Fuel Economy Full Synthetic 0W-20
High Mileage Full Synthetic 5W-30
High Mileage Full Synthetic 10W-30
Costco is not listed on the participating retailers, but as seen on SD they have worked with many other Mobil rebates in the past.