I would caution everyone against the automatic assumption that because Oil A has a TBN of X (higher) that it will go a longer OCI than Oil B with a TBN of Y (lower). Take a look at the new 229.51 Euro Oils...they have a lower starting TBN but still go long oil change intervals. A long time ago one of our members--might have been Terry--advised that how slowly an oil's TBN decreases is important too, not just the starting number. So, you could have an oil with starting TBN of 8 that remains efficacious longer than one that starts at 10.