I went to the websites of the gasoline companies that sell gas on my commute, and took a look around until I found an address to email a question to. Some responded immediately, and some took some time until it got forwarded to an engineer. Texaco never responded, but BP, Sunoco and Citgo responded very quickly.
Depending on where you live, determines how much sulfur is allowed in the fuel. There are metropolitan areas around the US that have low sulfur requirements.
After Katrina, President Bush suspended the new EPA specifications which included the 30ppm requirements that were supposed to go into effect nationwide this year, but I do not know the status of that at this point.
I'm not sure about NJ, but IIRC NYC may have low sulfur, and if you are close, the fuel may come from the same refineries.
I spent a lot of time at the EPA site, and it certainly would be helpful if they made it a little easier to find information such as this.
I know it's not much help, but if you find some info, I'm sure there are many of us that would be interested in hearing about it.