Given all that has been said over the years, the best response is probably to change the question. Instead let us ask, What constitutes a synthetic lubricant? There is a difference.

Most people in our industry are aware of the landmark 1999 ruling on this subject by the National Advertising Division of the Council of Better Business Bureaus (NAD) in the United States – a decision that effectively opened the door for marketers to call engine oils synthetic if they were made with severely hydrotreated API Group III base oils. Previously, polyalphaolefin base stocks were the only basis of synthetic engine oil claims.

I dont intend to rehash all those technical discussions. Suffice it to say that the NAD decision and marketing policies resulting from it, while coming from a U.S. body, have by and large been adopted globally. One exception is Germany, where synthetic lubricants are still synonymous with use of PAO base stocks.

But the NAD did not clarify the position unequivocally – at least not for me. The decision accepted, based on industry submissions and expert witnesses, the argument that saturation, cracking, isomerisation and hydrofinishing processes used to make Group III oils cause significant chemical change, or synthesis, as the feedstock is upgraded to completed base stock. However, the same arguments could be applied, say, to Group II+ base stocks, which use essentially the same process line-ups and also undergo significant chemical transformations. Moreover, Group II+ stocks are only marginally different from the higher viscosity index Group III stocks.

Carry this to the next logical step and the same could be said of standard Group II stocks that use essentially the same process line-ups. Where do you stop? Even Group I base stocks have been made using severe hydroprocessing, catalytic dewaxing and hydrofinishing, although often these processes are not all used in the same production run, unlike with Group II and III. It is interesting to note that industry bodies such as the American Petroleum Institute and SAE have chosen not to get involved in defining of synthetic.

This is why it probably makes sense to heed the guidance in the NAD ruling, which essentially states that a synthetic lubricant (as opposed to synthetic base stock) is a lubricant for which the consumer has an expectation of superior performance. A synthetic lubricant has been formulated to deliver the levels of performance which can be achieved only by the use of judiciously chosen base stocks from a variety of sources, including severe reforming and cracking processes at a petroleum refinery.

Once the levels of performance aspect is established, this directs our attention to the finished lubricant and away from the base stock. In general, synthetic lubricants combine the desirable attributes of a high-quality base oil with directionally higher additive treat rates, leading in general to superior performance, whether this be oil drain interval, engine cleanliness or wear protection.

Does this mean that if we use a synthetic base stock we are guaranteed superior performance? Certainly not. It is still possible to use the additive components inappropriately or to under-treat the additive package in what are accepted as synthetic base stocks. Again, this underscores why we need to use the implicit definition based on the consumers expectation of superior performance of the finished lube, rather than any explicit technical definitions based on the base stock.

It is also unfortunate that synthetic terminology has not been reserved for marketing claims but has found its way into some countries fiscal positions and product coding policies on lubricants. With no global and unequivocal technical definition of a synthetic base stock or lubricant, there is tremendous room for confusion and inconsistency when moving lubricants between countries. There have been cases in country regulations where the terms synthetic base stock and synthetic finished lubricant have been used interchangeably and, hence, inappropriately.

So what would be a good way forward? In my opinion we should reserve the terminology synthetic solely for marketing claims for finished lubricants of superior do we mean by superior performance? Performance that is demonstrably better, using bench testing or field trials, than the basic minimum level of lubricant performance guaranteed by global lubricants industry bodies, mainly those in the United States, Europe and japan.

This then moves the discussion onto finished lubricants rather than base stocks. Since formulators like to make life easy for themselves, they will necessarily start development of such synthetic products with a very high quality base stock. This almost inevitably means PAO or high quality Group III or a mixture of the two. There is no other way for formulators to get the required combination of low volatility, low-temperature viscosity performance and antioxidant response that such products demand – at least not with hydrocarbon base stocks.