"Briefly, there are two types of “synthetic” oils on the market. Group IV oils consist of molecules that are synthesized from simpler chemical compounds. This lets the chemical engineers “tune” the characteristics of a lubricant to exact specifications. These oils flow more freely at extreme low temperatures and don’t break down at very high temperatures. As a side benefit, they generally can be specified one or two grades lighter than a mineral oil, which consumes less energy as friction inside the engine and saves fuel. These are superior products, and command a premium price. Mobil 1 is a good example of a high-end Group IV. Group III lubricants are made from reprocessed petroleum products normally left over after making crude oil into gasoline, diesel fuel, heating oil and other products. They’re more modestly priced, and have many of the desirable characteristics of the higher-priced spread."
Mike Allen senior editor at Popular Mechanics
"By the way, a lot of folks ask us about whether they should be using synthetic oil. Synthetics have a number of advantages over old-fashioned oil — most notably, they are less likely to breakdown when operating at high temperatures.
So, which should you use? Our advice is this: under most circumstances, we’d opt to use synthetic oil — in particular, if you have a high-end car, a high performance car, or if you happen to know that your model is prone to having the engine clog with varnish and other gunk. (Some Toyota V6 engines have been notorious for this problem.) In those cases, we’d recommend going the synthetic route.
If you’re already using traditional oil, and want to make the switch to synthetic, try using a blended oil which contains a mix of traditional and synthetic oils.
Synthetic oil remains a bit more expensive than regular oil. But, over the life of the car, the differential is probably not more than a few hundred bucks — and we think that’s worth it."
The Tappet Bros.
“RAY: So you certainly can go back to the synthetic blend next time. Or, you may want to stay with the full synthetic. It’s great stuff. It is more expensive. But because it lubricates so well and doesn’t break down as quickly as conventional oil, you don’t have to change your oil as often.
TOM:So that means we have fewer quarts of used oil to recycle or dispose of, fewer empty oil containers in our landfills and, not incidentally, less foreign oil we have to import.
RAY: And if you spend $40 on four quarts of synthetic and change it after 10,000 miles, or $20 on four quarts of a blend and change it every 5,000 miles, you end up spending the same amount – on the oil. But you save money on the filter and what you pay Pokey Lube for the labor. And you can skip the tailpipe polishing they inevitably sell you once they’ve got your car up on the lift.”
“Under dynamometer testing, Car Craft found in 2009 that Mobil 1 0W-30 generated an extra 10 to 15 extra horsepower over conventional 10W-20 and 20W-50 conventional oils… Much of that can be attributed to the overall lower viscosity of the tested synthetic, which results in less friction inside the engine than the higher viscosity conventionals. This is one of the advantages of synthetic oil—it can operate effectively at lower viscosities without breaking down…Your best bet for motor oil is a synthetic like Mobil 1, Valvoline SynPower, or Castrol Edge, which you can get for a moderate price if you hunt for sales and rebates.” Ed Grabianowski
“Finally, for those of you who drive your vehicle hard, tow a trailer, drive very short distances, sit idling and in stop & go traffic for long periods, live in a cold climate and/or if your car runs hot, quality synthetic motor oil, synthetic gear lube, and synthetic automatic transmission fluid is a wise investment that will provide the additional protection you require as well as last thousands of miles longer than conventional lubricants.” Don Stevens mechanical engineer, member of the Suncoast Region of the PCA and BMWCCA
What’s even more terrifying is found in this summary from https://www.hort.purdue.edu/newcrop/ncnu02/v5-029.html Get a load of this:
"Canola-based motor oils have rapidly evolved into a competitive product. In terms of pricing, they are highly competitive with synthetic motor oils. They are also the most “environmentally friendly” of the motor oils available maintaining properties of non-toxicity and biodegradability. In terms of functionality, they have exceeded expectations by surpassing both conventional and synthetic oils in the tests conducted. As a low friction fluid, these tests indicate vegetable motor oils, or bio-oils, are a competitive product in modern engine applications.
A pleasant surprise has been the response of engines in terms of tailpipe and manifold gas emissions. The reductions in nitrous oxides, carbon monoxide, non-methane hydrocarbons, and hydrocarbons provide an easy and effective way to reduce air pollution. The value of these exhaust emissions has now become established and, in effect, may have more value than the oil itself. The impact of conversion to a bio-based motor oil for each million automobiles driven 18,590,000,000 km per year (17,699 km per vehicle) would be staggering. Hydrocarbons from automotive exhaust would be reduced annually by 1,101 t; carbon monoxide would be reduced by 87,475 t; and nitrous oxides would be reduced by 1,416 t."