I'm surprised at the amount of people that actually get their oil changed in their vehicle one way or the other...
Everyone knows the most efficient way to ensure a clean supply of oil is to own a vehicle with a quart-a-month habit. You just pour half a quart of the cheapest 10w30 money can buy into the engine every time you get gas.
It's easy, it's simple... and your oils is ALWAYS fresh.
(filters are overrated)