We at Honda have been striving to develop fuel-efficient engine oils and applying them to models to have more and more fuel saving automobiles. To be more specific, the improvements have been done for mineral oil with High Viscosity Index (hereafter referred to as HVI) base oil. Our study with HVI base oil has continued and eventually led to development of an SAE 0W-20 grade engine oil that provides additional fuel savings. It showed a fuel economy improvement of 1.5%. Due to concerns about abrasion resistance and oil consumption related to the reduced oil viscosity, vehicle testing was conducted. That testing demonstrated these problems did not occur.Ultra low viscosity oil was studied separately. It has shown excellent fuel saving performance in innovative low friction engines designed with full consideration given to abrasion resistance.