While researching Amsoil I ran across this rather lengthy but informative paper on Synthetic oil.

I've included the first four paragraphs and the link to the rest of the paper for your viewing and learning pleasure.


Title: Synthetic Oil: Rx for Long Engine Life by Curt Scott

[Publishers Note: Since specialty car enthusiasts and street rodders
often tend to be zealots when it come to optimum care and maintenance of
their cars, and also because so many of these cars utilize smaller,
harder working engines, we at Homebuilt Publications felt that the
following article would be of particular interest to Specialty Cars
readers. Our own interest in the subject is personal as well as
professional, since we have firsthand experience with the benefits of
synthetic lubricants. One of our cars is a 1979 GM sedan whose odometer
and maintenance records reveal over 200,000 miles of driving, with never
a missed-beat of its 350 cu. in. gasoline engine, and which has never
once required an engine repair... not even a minor one! It still runs
as well as the day it was new, it's sparkling clean inside, and all
cylinders check out to original compression specs. For all but the
first 12,000 miles it has thrived on a strict diet of premium synthetic
motor oil, changed only once every 25,000 miles. When we began research
for this article, no one had to convince us that synthetics offer
distinct advantages.]

Many of the things we take for granted as conventional aspects of
twentieth-century life were unimaginable only a few decades ago. For
instance, who would have foreseen in the 1940's, that in the 1980s, tiny
electronic marvels called transistors would have effectively replaced
the unreliable vacuum tube, or that a single, miniature silicon chip
could duplicate the functions of an entire, roomsized digital computer,
or even that hundreds of different exotic and classic automobiles would
eventually be reborn and replicated in a new material called fiberglass,
for assembly by the owner?

So it is with the rapidly-emerging synthetic lubricant market. Those
naysayers who only a decade or so ago prematurely dismissed synthetics
as "snake oil" are now among the staunchest devotees of
laboratory-manufactured lubricants. Among these believers are top
lubrication engineers, race car drivers, vehicle fleet operators, and
millions of private motorists around the world. What factors have
contributed to the growing enthusiasm for synthetic lubricants? Simply
put, synthetically-produced lubricants have demonstrated beyond doubt
that they are far superior to their conventional petroleum counterparts
in fulfilling the many and varied tasks demanded of oil by today's
modern engines and power trains. Indeed, synthetic lubricant technology
is swiftly progressing to a point where it is possible that engine wear
may no longer continue to be the major limiting factor in the expected
life span of motor vehicles. An examination of synthetic engine
lubricants, along with a review of both laboratory and real world
comparative test results, will assist the reader to understand the
differences and the advantages offered by these state-of-the-art motor
oils.

The first question demanding an answer is: *Just what is synthetic oil*?
Technically speaking, synthetic lubricants are made by chemically
combining, in a laboratory, lower-molecular-weight materials to produce
a finished product with planned and predictable properties. Don't be
confused by this technical double-talk. What this means is that
synthetics are custom-designed products in which each phase of their
molecular construction is programmed to produce what may be called "the
ideal lubricant." This process departs significantly from that of
petroleum lubricants, whose physical components, both desirable and
undesirable, are inherited from the crude oil from which they are
refined. Crude oil possesses thousands of varieties of contaminants,
depending upon the oil's geographical and geological origins, which no
amount of refining can entirely remove. Corrosive acids, paraffins and
other waxes, heavy metals, asphalt, naphthenes and benzenes, as well as
countless compounds of sulfur, chlorine, and nitrogen, remain in the
finished product. Equally as important, petroleum oil molecules, as
contrasted to uniform-sized synthetic oil molecules, vary significantly
in size, shape, and length. When your engine heats up, the smaller
molecules evaporate, while the larger ones tend to oxidize and become
engine deposits. As a result, refined petroleum lubricating products
differ widely in their overall quality and performance. The presence of
and the resulting drawbacks of the undesirable constituent elements lie
at the very root of the considerable performance differences between
synthetic and petroleum-based motor oils.

Read the rest