1995 Buick Century Owner's Manual - Page 206

Fuel Use regular unleaded gasoline rated at 87 octane or higher. It should meet specifications ASTM D48 14 in the United States and CGSB 3.5-92 in Canada. These fuels should have the proper additives, so you should not have to add anything to the fuel. In the United States and Canada, it's easy to be sure you get the right kind of gasoline (unleaded). You'll see UNLEADED right on the pump. And only unleaded nozzles will fit into your vehicle's filler neck. Be sure the posted octane is at least 87. If the octane is less than 87, you may get a heavy knocking noise when you drive. If it's bad enough, it can damage your engine. If you're using fuel rated at 87 octane orhigher and you still hear heavy knocking, your engine needs service. But don't worry if you hear a little pinging noise when you're accelerating or drivingup a hill. That's normal, and you don't have to buy a higher octane fuel to get rid of pinging. It's the heavy, constant knock that means you have a problem. 1 NOTICE: If you try to do your own service work without knowing enough about it, your vehicle could be damaged. I 6-2