MTBE has been phased out in areas that require "reformulated gasoline". I am not sure what the current MTBE status is in the rest of the US, but it is still being used in many other coutries.
Other oxygenates: TAME, ETBE, iso-octane
Reformulated gasoline (RFG) is gasoline blended to burn more clearly than conventional gasoline and to reduce smog-forming and toxic pollutants in the air we breathe. The RFG program was mandated by Congress in the 1990 Clean Air Act amendments. The first phase of the RFG program began in 1995 and the second (current) phase began in 2000.
RFG is required in cities with high smog levels and is optional elsewhere. RFG is currently used in 17 states and the District of Columbia. About 30 percent of gasoline sold in the U.S. is reformulated.
(
Reformulated Gasoline (RFG) | Fuels and Fuels Addtives | US EPA)
Edit: Found this bit of info...
"MTBE is no longer allowed in gasoline dispensed at public pumps, however it may still be found in additives and in specialty racing fuel"