The Top Tier designation only applies to gasoline.

I got to thinking about your reference to Tier 1, as I had assumed you meant Top Tier. Tier 1 for diesels refers to a level of emissions standards for stationary engines. We are now up to Tier 4. Those standards are about emissions, not fuels (although ULSD will be required to meet the newer standards)

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2007 X3 3.0si, 6 MT, Premium, White

Retired:
2008 535i, 6 MT, M Sport, Premium, Space Grey
2003 X5 3.0 Steptronic, Premium, Titanium Silver
2002 325xi 5 MT, Steel Grey
2004 Z4 3.0 Premium, Sport, SMG, Maldives Blue