[Brian R.]

That study only holds true for the engine in the taxis and the type of driving they do. Most engines are harder on oil that the basic engine they order for taxi fleets. Taxis also keep their engine hot by driving and idling alot. They don't do short to-the-grocery store jaunts like some people do regularly.

There are a million ways to drive a car over its life. Everyone has to make their own decision about how much they stress and contaminate their oil, as well as find out if their engine is susceptible to causing their oil to degrade faster than normal. There is no right or minimum frequency for oil that fits everyone.