Royal Dutch Shell (through their Pennz & QS brands), has by far the largest share of the QuikLube market. The business model for these stores depends on oil changes (and selling additional services like wiper blades, air filters, etc), every 3k-5k miles. This is why Shell is so opposed to extended drains & why they have tied their engine warrantees to 4k changes. (They consider even 4000 mile changes a concession from their usual 3000 miles). Of course this puts them in the position of defending a position that's indefensible. For example, if 4k changes with Ultra are required for severe service, what about PP or PYB? Do these then require changes every 2k-3k miles? The whole concept is absurd....