How is engine oil made?

Without going into detail, engine oil is a mixture of a base oil and additives. The base is obtained either from crude oil (mineral automotive oils), through chemical synthesis (synthetic automotive oils), or by blending mineral and synthetic bases in various proportions (semi-synthetic automotive oils). On its own, the base has a basic set of lubricating and operating properties, but using it in an engine is impossible without adding various additives that account for the different operating modes and the engine's service life.

Additives are substances added to engine oil to strengthen, weaken or stabilise certain existing properties and characteristics of the oil, or to give the oil new properties needed for the engine to run normally.

The additives blended into engine oil during production handle a range of tasks — from stabilising viscosity at certain temperatures to cleaning the engine's internal parts. Engine oil manufacturers don't disclose the composition and properties of their additives — that's their trade secret — and, frankly, the ordinary consumer doesn't need to know it anyway. What matters is that the balanced set of these additives in a given brand of oil must meet certain standards accepted worldwide, as well as additional requirements for the oil's composition set by carmakers.

So it's precisely the balanced set of additives contained in a given engine oil that makes it suitable for use in some particular engine. And it's the engine designers, of course, who set the tone on these matters.