Just stocked up on Mobil Delvac 1300 15W-40 oil for my powerstroke for only $9 a gallon. It's even cheaper than Walmart's deal of $11/gallon. Stack that with the $6/gallon rebate that Mobil is offering (limit of 10 per household) and you're getting oil for $3/gallon! I always use Mobil rebates and always get paid within a month. Killer deal...especially considering how much oil diesel's use for a change.