Real long post I made on here in one of the old oil threads that gets into it a bit. This method is used by many fleet managers. It does require a few assumptions along the way... but as a large scale rule it works well. Similar to using "Running Hours" for metering equipment use/abuse.

 

Works perfectly for fleet setups since they generally run the same route in the same time period.

When I had a job 40 miles away, working 6 days a week, I simply changed my oil once per 2 months, and changed the filter every other oilchange. That was with my d15b2 civic with over 200k miles at the time. SuperTech 10w-30 in the summer, 5w-30 synth in the winter

 

Not exactly.. it has more to do with eliminating some of the variation in how a car can be driven using mileage intervals. 5000 rural interstate miles and 5000 miles on I355 are world's apart. Much more similar is the amount of heat and blow-by of a fixed 150gal being burned during the above forms of use, to put it simply.