I ran across this a few weeks back so I bought a few gallons. I think 4 in the max, but 5 dollars back a gallon is not too shabby. Looks like it's good thru the rest of 2016.
http://rotella.shell.com/coupons-rebates-and-sweepstakes/save-5-per-gallon.html
http://rotella.shell.com/coupons-rebates-and-sweepstakes/save-5-per-gallon.html