2003 GMC Safari Owner's Manual - Page 224

Some gasolines that are not reformulated for low emissions may contain an octane-enhancing additive called methylcyclopentadienylmanganese tricarbonyl (MMT); ask the attendant where you buy gasoline whether the fuel contains MMT. General Motors does not recommend the use of such gasolines. Fuels containing MMT can reduce the life of spark plugs and the performance of the emission control system may be affected. The malfunction indicator lamp may turn on. If this occurs, return to your authorized GM dealer for service. Fuels in Foreign Countries If you plan on driving in another country outside the United States or Canada, the proper fuel may be hard to find. Never use leaded gasoline or any other fuel not recommended in the previous text on fuel. Costly repairs caused by use of improper fuel wouldn't be covered by your warranty. To check the fuel availability, ask an auto club, or contact a major oil company that does business in the country where you'll be driving. 5-7