Leaded gasoline generally has a much higher
octane rating than
unleaded. Many people who own
classic cars originally designed to run on leaded gasoline now have to run the highest possible octane gas from the pump to get reasonable
performance.
Leaded gasoline is still in production and use. It is used, for example, as high performance race fuel at drag strips. Many strips have leaded gas for sale at pumps strip-side. Octane ratings of 100, 110 and 115 are not uncommon. The anti-detonation properties of race gas is not to be underestimated. Using leaded gasoline in a turbocharged engine is generally the most desirable thing to do when trying to stave off detonation during hard drag runs.
Leaded gas will however destroy oxygen sensors over a period of time. Most electronically-controlled engine systems now use these sensors. Therefore it is not a good idea to use it unless you like changing them fairly often. Leaded gas is also very bad for catalytic converters. It's also illegal for use on the street, so beware.