My wife and I just bought a 1 yr. membership to COSTCO this past weekend and I was looking at their oil. All they had was Mobil 1 in 6qt. cases for $26 and change and Formula Shell in 12qt. cases, I remember the unit price per quart for that came out to $2.19 a qt. Are those descent prices? Does COSTCO ever get other oils in, or is it mainly those two? I was planning on running Pennzoil Conventional in my wifes 96 explorer, but now that we got the member ship, I can by the Formula Shell for much cheaper. I know its pretty well reguarded here so thats why I'm considering it. Is it a 6,000mile oil with about a 50/50 mix of city and highway driving? I've been trying to cut costs since buying our first house and made the decision a while back to switch to conventional in both our vehicles