Regular Mobil 1 always get mentioned but for those of us with diesels there is a promotion for us as well.
List of participating retailers is in this link. Walmart isn't listed but it's always worked for the non diesel Mobil 1 rebates. I don't see why it wouldn't work for the diesel oil as well.
2017 Mobil Delvac™ fall promotion rebate terms and conditions
Between Aug. 1, 2017, and Dec. 31, 2017 (the "Promotion Period"), purchase Mobil Delvac 1™ ESP, Mobil Delvac 1™ LE, Mobil Delvac™ 1300 Super, or Mobil Delvac™ Extreme heavy-duty diesel engine oil products ("Eligible Products") from a participating retailer listed below ("Participating Retailer") and receive a rebate as follows:
For one (1) five (5)-gallon pail of Mobil Delvac 1 ESP or Mobil Delvac 1 LE synthetic heavy-duty diesel engine oil, receive a sixty-dollar ($60) rebate check by mail (the "$60 Rebate");
For one (1) one (1)-gallon jug of Mobil Delvac 1 ESP or Mobil Delvac 1 LE synthetic heavy-duty diesel engine oil, receive a twelve-dollar ($12) rebate check by mail (the "$12 Rebate");
For one (1) five (5)-gallon pail of Mobil Delvac 1300 Super or Mobil Delvac Extreme heavy-duty diesel engine oil, receive a thirty-five dollar ($35) rebate check by mail (the "$35 Rebate"); or
For one (1) one (1)-gallon jug of Mobil Delvac 1300 Super or Mobil Delvac Extreme heavy-duty diesel engine oil, receive a seven-dollar ($7) rebate check by mail (the "$7 Rebate").
The rebates used to be $25 for Delvac 1300. Now it appears to be $35 per 5 gallon bucket.
Best way to maximize this is to wait for the buckets to go on sale.
Currently O'Reilly's has it on sale for $69.95
Autozone has Delvac 1300 even cheaper for $64.99
To get the Autozone price down to $64.99 on the right click on "SAVE NOW" a little ways under the add to cart button. It will bring you to a new screen where you'll select between the 3 5 gallon buckets on sale. Choose the Mobil Delvac. I don't know if you can do this in store, previously every time I've done this the store has always told me it's online only so I had to stand in the store and purchase via the app, then wait for the order information to be sent to the store.
I don't know what the Mobil Delvac 1 sale prices are so I can't offer any input on them but you get $60 back per bucket.
Buying gallon jugs limits you to 5x$12 rebates for $60 or 5x$7 for $35.
With the 5 gallon buckets though you can get 2 rebates for 2 buckets. $60x2 or $35x2 depending on which oil you choose. Essentially getting 1 5 gallon bucket of Delvac 1300 for free when you buy 2 and get the rebates for them.