i do alot of diesel performance work(cummins, powerstroke, dmax) but i got the idea, why not start a mobile oil change service. in the 15 mile radius/area where i live, there are 2 quick lubes, owned by the same person, neither with good service or friendly workers(as said by so many people i know who went there). i developed a good rep in the community for auto repair/maintenance, and id like to be competetive with the quick lube places. id also replace air and fuel filters etc., if needed. would it be best to buy my oil in bulk from auto parts stores, like some 12 quart cases at a time? for conventional, id go with PYB (5W20, 5W30,) and Napa Gold filters, and recommend 4-5k ocis to my customers. for Synthetic, id go with quaker state and Fram XG.