You have to read the owner mannual. There it is explained what kind of gasoline you must use in your car. But, I think its the premium one. It depends of the engine , its power and the compression ratio.
The 2011 Mercedes-Benz SL-Class runs on premium unleaded (required).
The 2011 Mercedes-Benz GLK-Class runs on premium unleaded (required).
The 2011 Mercedes-Benz M-Class runs on premium unleaded (required).
The 2011 Mercedes-Benz S-Class runs on premium unleaded (required).
The 2011 Mercedes-Benz SLK-Class runs on premium unleaded (required).
The 2011 Mercedes-Benz E-Class runs on premium unleaded (required).
The 2011 Mercedes-Benz CLS-Class runs on premium unleaded (required).
The 2011 Mercedes-Benz C-Class runs on premium unleaded (required).
The 2011 Mercedes-Benz CL-Class runs on premium unleaded (required).
The 2011 Mercedes-Benz G-Class runs on premium unleaded (required).
The 2011 Mercedes-Benz GLK-Class has 24 valves.
The 2011 Mercedes-Benz SLK-Class has a V6 engine.