This oil category was driven by two new cooled exhaust gas recirculation (EGR) engine tests operating with 15% EGR, with used oil soot levels at the end of the test ranging from 6 to 9%. These tests are the Mack T-10 and Cummins M11 EGR, which address ring, cylinder liner, bearing, and valve train wear; filter plugging, and sludge. In addition to these two new EGR tests, there is a Caterpillar single-cylinder test without EGR which measures piston deposits and oil consumption control using an articulated piston. This test is called the Caterpillar 1R and is included in the existing Global DHD-1 specification.In total, the API CI-4 category includes eight fired-engine tests and seven bench tests covering all the engine oil parameters. The new bench tests include a seal compatibility test for fresh oils and a low temperature pumpability test for used oils containing 5% soot.This paper provides a review of the all the tests, matrix results, and limits for this new oil category. This work was completed by the ASTM Heavy Duty Engine Oil Classification Panel (HDEOCP) in October 2001, at a cost of $5.71 million (6.28 million Euro). This was followed by a successful ASTM D.02.B ballot in December 2001. API-licensed products designated API CI-4 will become available in August 2002.API CI-4 oils are pivotal components in maintaining diesel engine durability using cooled EGR. API CI-4 is a higher quality oil than the previous diesel oil categories, so it will provide engine protection for both existing and new EGR engines.