Mobil 1 synthetic oil was launched in Europe and Japan in 1973, and in North America a year later.
(Two years after AMSOIL oil received API-rating for the FIRST SYNTHETIC OIL). Initially available only in an SAE 5W-20 viscosity grade, the Mobil 1 line expanded during the next decade.
In 1992, a new formula was introduced that improved high-temperature engine protection. Advanced Formula Mobil 1 was launched in 1996, with improved anti-wear performance and lower phosphorous levels to increase the life of the catalytic converters that were fitted to every car in the North American market.
The evolution of Mobil 1 continued with the introduction of Mobil 1 Tri-Syntheticââ??¢ Formula in 1999. Tri-Syntheticââ??¢ combined three high-performance synthetic fluids with a package of performance additives.
In 2002, Mobil 1 with SuperSynââ??¢ is introduced. With a combination of high-performance fluids, plus the SuperSynââ??¢ anti-wear system.
(This is the point where it was being referred to as a true or 100% synthetic by folks in the industry.. I still haven't found a valid reason for that comment, unless untill that time it was really a blend?) 
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