The API protocol was simple. It categorized base stocks according to three parameters considered important for engine oil needs: sulfur,saturates and viscosity index (V.I.). Although it may not have been APIs intent, for all practical purposes these parameters effectively established quality buckets based on refining technology.

Solvent-refined base stocks, with more sulfur, less than 90 percent saturates content and lower V.I., were defined as Group I. Hydroprocessed base stocks (less sulfur,more saturates, higher V.I.) formed Group II, and Group III at first included all other types of base stocks. Just two years later,in 1995, API redefined Group III as hydroprocessed base stocks with V.I. greater than 120. It also added two new groups: Group IV included only polyalphaolefins (PAO), while all other stocks -naphthenics, esters, glycols, whatever -were dumped with a shrug into the Group V bucket.

After API established these groups, there was peace in the base stock world, but it didnt last long. Group III wasnt satisfied just to have its own API category. It wanted to capture new territory and drape itself in the noble robes of a Group IV,calling itself asynthetic just like PAO. Although there has never been an armistice, Group III did appear to win this war and is now commonly accepted as a synthetic base stock.

While this occurred outside of API, it nevertheless blurred the base stock guidelines. Since then, the API groups have continued to evolve unofficially. To understand how much adaptation has occurred, take a look at Chevrons webpage. It points out that the API groups have been informally subdivided to now include Groups I+, II+ and III+. As Chevron sees it, Group I+ still has high sulfur and low saturates, but its V.I. is in the range of 100 to 105. The company defines Group II+ as base stock with a V.I. in the range of 110 to 120. And although Group III+ is not yet commercially available, it suggests, These will be available in the second half of this decade, made from gas-to-liquid processes.

Not everyone agrees with these ranges, however. One recent U.S. patent said that Group II+ is a term used increasingly to describe Group II stocks of higher V.I. (110 to 119) and lower volatility than typical Group II stocks. Another viewpoint says Group II+ should have a V.I. in the range of 108 to 115. And although Chevron has little to say on how to define a Group III+ base stock, others are plunging in. Exxon Mobil, for example, has suggested that a Group III+ base stock will have a V.I. greater than 130.

Lets refer to Wikipedia, the infamous, open-source online encyclopedia. (You know,the one that pops up first on any Google search and that everyone uses to get the facts.) According to Wikipedia – now apparently the authority on base stocks – the lubricant industry commonly stretches the API Base Oil Group terminology to include:

Group I+, with a Viscosity Index of 103 to 108.

Group II+, with a V.I. of 113 to 119.

Group III+, with a V.I. above140.

There you have it, an authoritative definition of Group I+, II+ and III+. No need to check with any other experts.

And what to make of claims that a particular passenger car engine oil is made with Group II+ base stock? How to know its not really a less-stable Group II-, or even a Group II+/-instead? Can we get data showing a decrease in alkanes, increase in polyaromatics, and the methylene concentration measured from the overall carbon species in the base stock? What good would that do?

And what to do with this epiphany Ive had about how arbitrary base stock groups have become? Maybe Ill blend some of that less-stable Group II-stock with an API Group V pale oil, add a little API Group III, and trademark it all as Group VIII+. That sounds like a much better quality level than a Group II+ or API Group III.

And since API seems to be looking the other way -and has turned the definition of base stock groups over to marketers, Wikipedia contributors and others -maybe I can even charge a premium for this juice.