General Motors issue their own sets of requirements for service fill engine oils used in their vehicles. These specifications detail the viscosityA measure of a fluid's resistance to flow. A fluid with a higher viscosity flows less easily. grades and physical, chemical and engine testing that must be conducted in order to obtain an approval.

There are two separate specifications, dexos1™ for gasoline engines and dexos2™ for diesel engines. In Europe, dexos2™ is also used for service fill gasoline engines. All applications for approvals against GM’s dexos specifications are made through the Center for Quality Assurance (CQA), who administer the approval process on behalf of GM.