This sample of Mobil Delvac 1300 Super 15W-40 engine oil does not meet the minimum API CK-4 requirements or the Volvo/Mack or Cummins OEM requirements, the company said in a report accompanying its press release.

ExxonMobil insisted that the product has passed the Volvo T-13, as well as other required tests.

ExxonMobil stands by the quality of our products and has reaffirmed to our distributors and customers that Mobil Delvac 1300 Super 15W-40 carries valid OEM approvals and API CK-4 licensing, spokeswoman Sarah Ashlee Nordin told Lube Report yesterday, adding that Volvo confirmed the product still has its approvals for the Volvo VDS 4.5 and Mack EOS 4.5 specifications.

Observers called the statements unusually provocative for the lubricants industry.

I would say this is the most remarkable public display of data that Ive seen [in the lubricants industry], said Mike Jennings, principal of Abafor Lubricant Consulting, of Baltimore. They are saying, This oil clearly does not meet the standards, and here is the data to prove it. Its more aggressive and higher profile than anything that I recall seeing.

Shell is the worlds largest supplier of finished lubricants, and ExxonMobil is second largest.

In its press release and accompanying materials, Shell said it routinely purchases and tests sample of competing engine oils in order to compare them with its own products. It said it purchased a container of Delvac 1300 Super 15W-40 earlier this year and had it tested by an independent lab in February.

The Volvo T-13 is an engine test that runs for 360 hours and is designed to gauge an oils ability to avoid breaking down during prolonged exposure to high temperatures. Performance is tested two ways: by measuring the oils kinematic viscosity at 40 degrees C during the final 60 hours of the test; and by using infrared spectroscopy to measure degradation.

According to Shell, the Delvac sample exceeded the spectroscopy limits for the API and OEM specs by shortly after 300 hours. All kinematic viscosity limits were exceeded by around 350 hours. Shell said its own Rotella T4 15W-40 remained under all thresholds for the full 360 hours.

API lists Mobil Delvac 1300 Super 15W-40 as being licensed to display trademarks indicating that it complies with CK-4. ExxonMobil claims that the product also has approvals for original equipment manufacturer specs Volvo VDS 4.5, Mack EOS 4.5 and Detroit Diesel DFS 93K222 and that it meets the requirements of Cummins CES 20086. Shell said the Volvo T-13 is a required test for each of those specs and that sample in question failed to achieve passing scores for any of them.

Industry observers expressed different opinions about how much testing is warranted to support conclusions of oils failing to meet performance standards.

I think it leaves lots of open questions about how the testing was handled to reach this conclusion, Petroleum Quality Institute of America President Tom Glenn said. As head of PQIA, Glenn regularly contracts laboratories to conduct tests on samples of lubricants that his company has procured and reports on. In the past he also managed a large commercial lubricant testing laboratory.

If we had an oil that failed a test, the lab would run the test a second, and sometimes third time or more before taking the result to the client. He added, When PQIA has a product tested and it fails the first test, standard operating procedure is for PQIA to request that the laboratory recheck the results. He contended that retesting is particularly important for tests procedures with comparatively low precision and accuracy.

Of course, understanding the T-13 test costs close to $200,000 every time its run, this likely played into the number of times the sample was tested and the number of laboratories that tested it prior to Shell going public with the claim of failure.

Jennings, who specializes in technical aspects of heavy-duty diesel engine oils, said that retesting might not be necessary after a failed result. Every specification will have a threshold limit that must be achieved in order to pass the test, he said. But to account for statistical variability, the spec will also define a band with a limit above and below that number, and if the result falls within that band the oil is considered to have passed the test. If the result falls outside that band then yes, that one result is enough to conclude that the oil failed the test.

Shell told Lube Report that it conducted oxidation bench tests on Delvac 1300 Super 15W-40 samples pulled from six locations around the country and found consistent weakness in oxidation performance. The lab that it contracted conducted just one engine test.

The results indicate that the sample of Mobil Delvac 1300 Super 15W-40 failed the test, even taking into consideration the reproducibility limits and thus are considered statistically significant and accurate as validated by the independent lab, a spokesman said. Therefore, we did not feel that running a second test was necessary.

Shell appears intent on leveraging its claims for commercial benefit. In addition to the press release, the company plans to hold a webinar on them today for Shell distributors and customers. The company said it is conducting a campaign that will also include digital, social media and print assets.

ExxonMobil indicated it will not sit by idly.

ExxonMobil cannot address the specifics of the test results Shell produced, because we do not have the data, but we are conducting a thorough investigation, Nordin said.

Observers speculated that ExxonMobil might take Shell to court. While it is uncommon to see the lubricant manufacturers doing direct comparison of product claims based on data and naming names, Glenn said some in the industry would like to see more of it.

Its not infrequent for me to hear distributors say, I would like to see our supplier do more direct comparisons of test data on brands by name rather than referring to them by coded numbers or letters, he said.