When it comes to shopping for synthetic oil these days, you could be buying apples when you think you’re buying oranges.

A reader asks: We’re currently using Idemitsu 0W-20 full synthetic at less than half the price of Amsoil Signature Series 0W-20. Idemitsu is the OEM supplier for Honda/Acura and Subaru 0W-20 in Canada so their quality is not in doubt. Looking at your prices why would we bother changing?

Answer: Forgive us, but this will be a long answer. First, “OEM supplier” doesn’t necessarily imply elite quality, regardless of whose name is on the label. To us, OEM means “adequate quality that can deliver a healthy profit margin”. Second, if that 0W-20 is less than half the price of AMSOIL’s Signature Series 0W-20, you can bet your last dollar that it is not in the same category in terms of base oil or additive package strength. AMSOIL Signature Series 0W-20 is a world-class standout by any measure that hardly belongs in the same conversation as an OEM-quality offering. But let’s go further down this road today.

Yes there are deals on synthetic oil out there. There will always be cheaper products than AMSOIL out there. But is cheaper always better? Are all synthetic oils more or less the same? The answer is “no” to both questions.

Unfortunately the motor oil industry is not regulated with respect to what exactly constitutes a synthetic oil these days. Labeling a motor oil as “synthetic” doesn’t necessarily mean that the oil is the bottle is 100% synthetic as it may have 20 years ago. To provide context to this discussion, here is a brief definition of each base oil category. The base oil makes up about 95% of the motor oil. Additives like detergents, friction modifiers, anti-wear agents and corrosion inhibitors makeup the rest of the motor oil composition.

Group I– The lowest quality and least expensive base oil type. Group I oils are conventional oil (also known as mineral oil) as they are derived from crude oil.
Group II– This type goes through a more extensive refinement than Group I. Group II base oils are the most common conventional oil types on the market.
Group III– This petroleum base group undergoes higher refinement than Group II oils and is refined to the point where it can be categorized as “synthetic”.
Group IV– Known as polyalphaolefins or PAO, this group is synthesized in a lab not refined from regular petroleum or crude oil. Known as a true synthetic by purists.
Group V– For motor oil purposes, this group tends to be comprised of esters. This group is also a developed in a lab and not derived directly from crude oil. Also considered a true synthetic.

Of these base oil groups, Group IV and V are considered full synthetic in the traditional sense of the term. Group I and II are considered to be conventional or mineral oil as they are derived directly from crude oil. Group III tends to fall somewhere in between synthetic and conventional oil, depending on who you are talking to. Group III’s steady creep toward classification as a synthetic motor oil has created a very murky marketplace and is vital to this discussion.

Group III was not considered a synthetic base oil at one time. But in the late 1990s, Castrol started using Group III base oils in their motor oils that were marketed as full synthetic. Switching from a Group IV base to a Group III lowered Castrol’s input costs dramatically and Mobil launched a legal challenge against this practice. Castrol prevailed in this case as it was decreed that although Group III base oils may be derived from non-synthetic petroleum oil, they are processed to a degree that does not exist in nature. Therefore it can be deemed as “synthetic”. This ruling turned the motor oil industry on its ear.

Today the vast majority of synthetic oils on the market are formulated with Group III base oils. This in itself isn’t always a bad thing as a good Group III base blended with a competent additive package can perform at level a level that is not far from Group IV synthetic motor oils.

The problem for the consumer is that this slippery slope of playing fast and loose with the “synthetic” oil definition has only gone downhill. Industry experts are suggesting that it is possible for unsavory motor oil makers to produce oils that may be mostly Group I and II oils and label them as synthetic. The motivation to fudge on base oils is high as Group II base oils cost about a third less than Group III oil. Group IV and V base oils are considerably more costly. To widen profit margins, skimping on base oils and additives is an obvious way for bean counters to hit their profit targets. We have nothing against making a profit, but we do have a problem with false representation. If a synthetic motor oil has a price tag that is as inexpensive as a conventional oil (or close to it), you can bet that the base oil is Group III (at the very best) and have an additive package that is sparse.

There are no industry watchdog agencies that police this issue. While the American Petroleum Institute (API) decides which oils meet their specifications; they do not oversee how a product is labelled and marketed.

We have seen marketing literature for a semi-synthetic motorcycle oil stating that it “contains 10% synthetic oil”. At least they were being honest. Semi-synthetic implies half synthetic to many consumers and that probably almost never the case. Could this motorcycle oil be comprised of Group I and II base oils with just 10% Group III? It could be and no one can call them on it.

For full disclosure, we should point out that we carry a couple of Group III products. Notably the AMSOIL XL Series and OE Series of passenger car/light truck motor oils are formulated with Group III base oils. But as AMSOIL uses top-shelf base oils and very robust additive packages, we proudly promote them. The XL products are designed to stay in service for up to 10,000 miles (16,000 km) and OE products are good for the longest OEM drain intervals in the industry. This makes them a cut above the vast majority of engine oils that call themselves synthetic these days. We assume that the high-end AMSOIL Signature Series uses Group IV base oil, but AMSOIL refuses to disclose any formulation information. As the Signature Series oils have a suggested oil change interval of 25,000 miles or one year, there won’t be much room for compromises and short cuts.

To sum up, our reader contends that AMSOIL is too expensive. But expensive relative to what? The market is flooded with cheap synthetics that may barely qualify as synthetic. Yes there are cheap synthetic oils on sale at Auto Zone and Canadian Tire, but keep in mind that a good synthetic oil requires expensive ingredients. Our AMSOIL motor oils are not the cheapest, but they work very well. In 15 years of selling these products, we’ve had zero complaints about performance or quality. We have received a ton of positive product feedback. We’ll take that over the cheapest price any day.