In the UK we have Ultra Low Sulphur Fuel

http://www.greenergy.com/products/petrols.html

http://www.wipo.int/pctdb/en/wo.jsp?KEY=02/18521.020510
The feature of the invention is that the use of a low sulphur fuel enables the amount of anti-wear agents containing phosphorus such as eg ZDDP to be ha**ed without any adverse effect on the antiwear performance of the lubricating oil.

Is the fuel quality a major player in the general ZDDP reduction?