As of June 1, 2006, at least 80 percent of on-road diesel fuel refined in the Unites States must be ultra-low sulfur diesel. This means it must contain less than 15 ppm of sulfur. Some have compared this event to the requirement that removed lead from gasoline in the 1970s.

The new fuels will contain 97-percent less sulfur and will be available nationally at retail outlets by Oct. 15, 2006. Just as lead was a problem for the catalytic converters that clean car exhausts today, sulfur quickly hampers the proposed diesel exhaust filters' ability to remove contaminants.

Today's diesel engines produce one-eighth of the tailpipe exhausts of a truck or bus built in 1990. With the new controls and fuel requirements, it would require 60 trucks built in 2007 to equal the soot exhaust of one truck built in 1988.