There is much interest in reduced phosphorus due to the latest GF-4 sepcs. This was posted in a "zinc" thread but since we have wide interest in this topic, I thought I would also post it here: Phoshorus is one of the antiwear/antioxidant elements in the Phosphorus/Sulfur/zinc molecule of ZDDP. The sulfur atom of ZDDP is the activation atom for metal bonding, and provides a slight FM effect. ZDDP's have been used since about 1950 as the primary antioxidant/antiwear agent in engine oils, and are the main source of phosphorus in lubricants. The Sequence IIIC test in the '70's led to the development of oils containing high levels of phosphorus (0.14 mass %). High phosphorus oils can lead to deposits of phosphate on the surface of rare earth element catalysts in the catalytic converters. It has also been discovered that the interaction of metal detergents with ZDDP and their decomposition products can affect catalyst efficiency. However, the effects depends on the type and relative concentrations of metal and ZDDP in the oil. In addition, ZDDP's contribute 15-20% of the sulfated ash content of a fresh oil. Reducing the ZDDP should also result in lower piston/ring deposits. What you're going to see are new ashless antioxidants and AW/EP adds come into play now, such as alkylated diphenylamines (antioxidants), hindered phenols (antioxidants), and new AW adds such as boron esters, concentrated calcium and synthetic AW/EP adds (such as new esters). A newer type of zinc antioxidant/AW additive is ZDTC, or Zinc dialkyldithiocarbamate, which is similar to Moly DTC and Antimony DTC, and only varies as to the metallic element.