This week's show isn't on their web site yet, so I can't link. A lady was driving a friend's car across the country-- every state I think. The friend's only stipulation was that she do oil changes with Mobil 1. The caller had trouble finding Mobil 1. Tom and Ray's comment was that there were other synthetics out there, they thought Castrol made one, and to just go ahead and use that, no one would know the difference!