Ethyl Corporation’s Review of the AAM/AIAM Fleet Study 
Vehicles fitted with advanced emission control systems performed well with MMT®
  •     All of the test vehicles met applicable emission standards.
  •     Catalytic converters, spark plugs, oxygen sensors and OBD-II systems performed as designed.


MMT® had no negative effect on vehicle fuel economy.
  •     Test results are consistent with previous fleet test results: MMT® does not cause the failure of emission control devices or an increase in vehicle pollutants.

The study confirms Ethyl’s view that MMT® protects emission control systems from phosphorus and sulfur combustion debris that can degrade catalysts and components.

  •     Oxygen sensor and catalyst conversion performance was indicative of the established
MMT® scavenging mechanism for phosphorus and sulfur.


The air-fuel ratio in the MMT®-fueled vehicles remained closer to the original design and the reported fleet emissions trends are consistent with the greater lean shift experienced by the base-fueled vehicles.

The MMT®-fueled vehicles performed well despite numerous flaws in the study design and questionable maintenance practices  

  •     The study did not follow the fleet testing protocols endorsed by the auto industry in previous studies and ignored most of the recommended changes made by reviewers.
  •     The extreme driving cycle used in the study reflects accelerated aging conditions. The driving cycle had double the aging factor compared to severe consumer driving (95th to 99th percentile).
  •     The AAM engaged in questionable maintenance practices that included performing major repairs on a base-fueled vehicle and not on its MMT®-fueled partner vehicle and failing to perform maintenance on MMT®-fueled vehicles with significant mechanical problems.
  •     The low emission vehicles assigned to run on MMT®-fuel had lower fuel economy and higher CO2 emissions than the base-fueled vehicles before any mileage accumulation on the test fuels. This initial bias was maintained throughout the course of the study and suggests that the two fleets were fundamentally different.

An independent statistical review by Environ supports Ethyl’s assessment

  •     The performance of vehicles using MMT® -fuel was not statistically different from the performance of vehicles using base-fuel.
  •     The AAM’s conclusions are based on flawed and inappropriate statistical analysis.
  •     The AAM’s analysis ignores confounding variables and incorrectly attributes all differences in emission performance to the presence of MMT®.
  •     Vehicle design and variability dwarf all other factors impacting vehicle emissions.