This is kind of inverse to the discussion about the economics of using Mobil 1 vs. a more expensive synthetic oil. Since Mobil 1 is such a standard here, let's compare it to an excellent dino oil, like Castrol GTX or Pennzoil Purebase. For the price of one bottle of Mobil1, usually about $4, one can purchase 3 bottles of GTX. Conservatively, Mobil1 should last 10K miles. Let's be more conservative and say 9K miles. For the price, I can get 3 changes of GTX, lasting 3K miles each. OK, you also have to factor in the filter. To be fair, for the GTX changes, the filter is changed every 3 changes, meaning some old oil is left in there with new GTX oil. Does it matter much? Considering the scenerio above, would using GTX (or some other good dino oil), and changing it more often, be better for the engine than using Mobil1 for an interval 3x as long? Or, to put it another way, does Mobil1 last 3 times longer than the best dino oils?