On the West Coast, any diesel that contains bio has to be labelled. I've never had a problem finding stations that have no bio. I have noticed that 20% bio tends to be cheaper than 100% dino, so if you are on the cheap side, always check.
Its true that it has to be labeled as such, but as Russ61 noted from the Costco rep above, there's no way to guarantee the purity of fuel due to different spec fuels being pumped through shared equipment.
What happens is this....a regional refinery has a pipeline that might distribute gasoline that goes to Shell trucks on Monday morning, and on Tuesday morning, that same pipeline is feeding Chevron trucks, and on Wednesday morning, its filling up BP trucks, and then Shell again on Thursday morning, and so on.
Believe it or not, all petrochemical companies buy fuel from each other all the time. If there's Shell refineries in California but none in Texas, and Texaco refineries in Texas but none in California, then these competing companies will happily buy fuel from each other because its much cheaper to buy local fuel at wholesale than regularly transport their own refined products across 4-5 state lines.
Each brand has different proprietary additives and there's no way to guarantee that one doesn't mix with another. However, what happens in between these is interesting...that's when the smaller brands and non-name brands buy their fuel for a discount. So in between these big brand buyers, generic brands X, Y and Z are buying the wash out 'leftovers' from any number of brand name fuels. This ensures that enough additive-free fuel is able to wash through the equipment lines so that Chevron doesn't get upset about finding BP additives in their fuel, or vice versa.
Ultimately, though, it doesn't really matter, as all of these additives in fuel are compatible with each other and we as consumers mix fuels all the time. What one may notice, however, is that fuel from less-well-known brands and privately owned stations usually doesn't have as strong an additive pack as the heavily marketed and more expensive name brands.
In my experience, however, its never in recent years been a problem for me to run cheap fuel from a station
that has high turnover, but then occasionally run a fuel system cleaner to clean out any deposits in the injectors, fuel lines or fuel pump for both gas and diesel engines. For me, the money saved with always running cheaper fuel seems to exceed the occasional cost of bottled additives like techron concentrate or BG244, but YMMV depending on the fuel available locally.
