For the past thirty years heavy duty diesel oil performance has been defined by the API CD category type tests. During this time the trend in CD oils has been toward lower ash and lower TBN. This has been largely due to the performance improvements of ashless components which now form a major part of today's HD formulations. PC-1 type category testing indicates that ashless components will continue to be effective in meeting these higher heavy duty diesel targets. As a result, lower ash PC-1 type formulations are feasible.Oils have been developed using the dynamometer engine tests currently being worked with to define PC-1 to meet the target of improved oil consumption. These oils are also showing similar advantages in field performance testing over current CD/SF quality lubricants.