To expand on this further, Ford, in their manuals state (up until 2014):
Originally Posted By: Ford
Engine oil need only
meet the
requirements of Ford specification WSS-M2C945-A and display the API Certification Mark.
Your engine has been designed to be used with Ford engine oil, which gives a fuel economy
benefit while maintaining the durability of your engine.
Which means of course that the oil doesn't have to be
approved by Ford, it simply needs to meet the requirements.
Which is very different from what
Mercedes states:
Originally Posted By: Mercedes
Mercedes-Benz has very specific engine lubrication requirements and
only oils that have a MB approval number and the approved viscosity ranges are to be used when servicing your engine. The MB approval number is marked on the oil container similar to Figure 1. Verify the correct MB approval number on the individual oil container or accordingly for oil available in bulk quantities.
Audi is similar:
Originally Posted By: Audi
Oil Quality
All Audi engines must always use engine oils that conform to the applicable Audi Oil Quality Standard. No other
engine oils may be used. This also applies when topping off engine oil between services.