S15 (ULSD) is defined by the U.S. Environmental Protection Agency (EPA) as U.S. diesel fuel with a sulfur content not to exceed 15 ppm (parts per million). S15, S500, and S5000 are designations for diesel fuels that meet 15 ppm, 500 ppm, and 5,000 ppm maximum sulfur content, respectively, as defined in the American Society for Testing and Materials (ASTM) standard D975 Table 1. In different regions of the world ULSD may refer to different maximum sulfur content values, but ULSD and S15 are often used interchangeably in North America (U.S. and Canada).The S15, S500, and S5000 designations also apply to the Canadian diesel market.

When are we required to use it?

In the United States we are required by law to have this fuel at the pumps by October 15, 2006. Canada has also recently transitioned to ULSD.

So What?

If you already have a diesel engine there is not a so what, BUT, if you are thinking of buying a new RV with a diesel engine you need to be aware of a few things.
• The law requires new equipment on new diesel engines to help lower emmissions and this new engine will cost somewhere between $5,000 and $15,000 additional.

• The pre-2007 standard engines will burn the ULSD and do not need the extra equipment (grandfathered in to old emmission standards).

• The new engines (2007 standards) will not burn the older low sulphur diesel - they only burn the ULSD - in the USA that will not matter, but Canada has no regulatory compliance date set so you may have an issue getting fuel outside the USA.

You may want to get a pre-2007 standards engine. Many of the RV manufacturers' are telling us that they will be able to build for a while with stockpiled pre-2007 standard engines. If you want to save money and retain flexibility in fuels you will want to buy before they run out of pre-2007 standard engines.