Have seen several references to Pennzoil as a high quality conventional oil. But nothing much about Quaker State. Pennzoil-Quaker State are both owned by Shell Oil Co. I have been using QS 10W-30 in my 2002 Trailblazer 4.2 I6 since its first oil change. I "enrolled" it in the QS 10 year-250,000 mile warranty deal. Is there any significant difference between Quaker State and Pennzoil 10W-30 regular oil?