For the last 10 years automobile lubrication has been evolving. Within the last few years many of the biggest car makers have developed specific oils for their engines.
Oil changes used to be done with 10W30, 10W40 or in some cases synthetic oil. Now GM, Ford, Saab, BMW, Audi, Volkswagen and Mercedes Benz all have specific engine oils. Synthetic is a generic term that has lots of different meanings in different parts of the world. In North America it's meaningless. There are many cheap synthetic oils that can't pass these more stringent ratings.
