Top Tier is relatively new term in regards to gasoline and diesel fuel. The original intent was to be of a benefit to both suppliers and end users by providing a specialized marketing term to identify fuels which have been modified or upgraded from the accepted standard quality to meet OEM expectations.
To achieve 'top tier' status a supplier must pay a registration fee with the understanding that they must utilize an acknowledged superior detergency in their fuel in the manufacturer's recommended dosage rate. Including the increased amount of superior detergency is the only requirement.
In Diesel Fuel:
"Top tier' status for diesel fuel has significantly more expectations that that required for gasoline. In order to proclaim 'top tier' diesel fuel sellers must include deposit modifiers, lubricity, stability, and additional protections against particulate and water contamination. This last requirement is satisfied with the implementation of 10 micron filter on low flow (or a 30 micron or smaller on high flow) pumps.
In both instances, as long as the registration fee is paid, there are no testing results or proof that the additional improvements have been implemented required for marketers to claim 'top tier' status. Only an affidavit of compliance submitted with each application. The fee is based on the amount of 'top tier' designated gallons sold. It is up to the customers or end users to pursue quality assurances from the seller.
At this time there is no program for confirmation of 'top tier' compliance and adherence.