Group III oils are generally considered to be superior to Group I and Group II stocks, which have higher levels of aromatics and other impurities and lower viscosity indices. Group III constitutes a smaller portion of global supply than the two lower grades, but its share is growing faster, with several expansions and new plants having come online in recent years, and more projects planned in the next few years.

The driving force for Group III oils comes largely from the automotive lubricant market, where original equipment manufacturers and consumers are demanding engine oils that last longer and better protect equipment. Environmental concerns are also a factor, spurring demand for lubes that help both to improve fuel economy and to reduce air emissions.

Employing Group III stocks in engine oils can, however, cause companies to incur significant expense. The American Petroleum Institute and ATIEL are the principal certification bodies in North America and Europe, respectively. In general, they do not allow formulators as much freedom to substitute one Group III stock for another in a certified engine oil as they do with Group I and II oils. The exception is that API does allow a considerable level of Group III interchange in passenger car engine oils.

Interchange rules are important practical considerations as the price tag for a full battery of engine oil tests can run into the millions of dollars or euros.

During a Feb. 15 presentation here at the ICIS World Base Oils Conference, Lithcon Petroleum’s Lubricant Base Stocks Technical Manager Ernest Henderson explained it is no secretwhy thecertification organizations are less lenient on Group III interchange. API and ATIEL both require extensive testing before adopting interchange guidelines to ensure that base oil substitution will not impact oil performance. Sufficient documentation exists for Group I and II stocks because they have been used much more.

There seems to be growing consensus that the industry needs more Group III interchange rules.

The [engine] oils that are based on Group III will become more and more common, said Sylvain Leblanc, marketing manager in Europe, the Middle East and Africa for lubricant additive supplier Infineum UK Ltd. It is very clear that in the future we will need some kind of rules for [Group III] interchange.

Steps are underway. API has begun to discuss how to develop guidelines for Group III stocks. Henderson said a growing amount of test data exists to help document when and how it is safe to interchange one base oil for another – and when it is not. ButLeblanc and other agreed that much more remains to be done.

API is now generating data, Henderson noted. In Europe, there are hydrocracker-bottom-based and paraffin wax-based Group IIIs, so the data is essential.

Speakers at the conference expect that the door to interchangeability will be opened quickly.

[Group III interchange rules] have got to be based on data, said Alison Fisher, global business manager for heavy duty diesel engine oils at Lubrizol Corp. We have to protect the quality of the products.

Henderson suggested the industry may be ready for a new approach to interchange guidelines – one that allows substitution of oils that share certain chemical properties, rather than just a group categorization. Group I, II and III definitions are based on saturates levels, sulfur content and viscosity index. Group I oils are those that contain more than 10 percent aromatics or more than 0.03 percent sulfur. Group IIs have at least 90 percent saturates and no more than 0.03 percent sulfur but viscosity index 119 or less. Group IIIs meet the same saturates and sulfur minimums but have higher viscosity indices.

Others agreed on the need to define interchange rules differently – and warned that doing so could further draw out the wait for Group III guidelines.

We are trying to move toward property-based guidelines, said Alan Outhwaite, manager of business development for Chevrons global base oils operation. But its a very slow process.