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In the United States, gasoline is typically sold in three grades: Premium, Plus, and Regular. The main difference among these three grades is their Octane rating, which essentially measures how knock-resistant the fuel is. In order for the energy to be generated, fuel is mixed with air in the internal combustion engine. In theory, the fuel mixture should only be ignited by the spark plug at a precise time in the piston’s cycle. If the mixture is ignited at the wrong time, a “pinging” sound called “knocking” maybe heard. The consequences of knocking vary from just being annoying to faster wear-and-tear to completely destructive to the engine. The Octane rating describes how easily the fuel will ignite. The more easily it ignites, the more knocking can be expected and the lower the Octane rating. Premium gasoline has the highest Octane rating at 92 with Plus and Regular following at 89 and 87, respectively. The grade difference has nothing to do with energy density of the fuel. There is no added benefit to using a higher grade than required by the manufacturer, since most engines use sensors to eliminate engine disruptions caused by knocking.

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April 17, 2011