CARB is the government agency that regulates air quality in the state of California in the US.

From a refining stand point, CARB is important because it regulates the quality of fuels such as gasoline and diesel when sold in California.

The standards set by CARB for fuels are generally tighter than in the rest of the US resulting in a unique set of fuels grades in California called CARB fuels. These include CARB gasoline (CARBOB) and CARB diesel.