*cough* *cough* Like almost every O'Reilly sale?
Right now they have their M1EP - $30.95 for 5 [or more] quarts. 1 quart bottles are the same price as 5 quart jugs. $6.19/qt. So let's assume your tax rate is 9%. $30.95 + 9% = $33.74. Now do O'Reilly's $10 rebate and Mobil's $15 rebate, and you're at $8.74 for 5 quarts of EP! No limit on O'Reilly's $10 rebate, limit 2 rebates ($30) per household on Mobil's $15 rebate.
Pro tip: I have 28 sets of rebates (140 quarts, $700) pending for both companies and counting. Pay cash and don't give your O'Rewards/phone number. Call them later on to add your receipt because "you forgot to give your number). O'Reilly just wants the original receipts and form mailed in, so I'll wait until I'm done buying to send them all off with one stamp. Mobil is all digital, and only wants a name, email, and address. I have plenty of unique emails, plenty of VPN IP addresses (just in case Mobil gets curious), and plenty of friends & family addresses. Basically, limits are for peasants.