All diesel fuel sold in CA meets BMWs spec for 'premium diesel cetane'.

Now, in terms of the other stuff in diesel fuel that provides for lubricity (ie good for your fuel system, pumps, injectors), there is virtually no way to know what is being sold... websites, links, marketing claims, etc... but in terms of "premium diesel" it is almost unregulated.... There are minimum standards, and then that's it- all the rest is hype and trust. Folks seem to think "Oh, they are a Top Tier gas company, must be top tier diesel too"