Amazon offers Pennzoil Platinum 5W-20 5-Quart Full Synthetic Oil for $22.65. Add it to your cart via Subscribe & Save to drop it to $19.25 and bag free shipping. That's $3.85/quart and the best price we've seen without rebate hassles. (It's a current low by $3.)

Note: Be sure to cancel your subscription once your order arrives to avoid being billed for subsequent shipments.