What is unleaded petrol?

Unleaded petrol is petrol which does not contain lead. There is no real reason to call it this now though, as we don't actually have petrol that does contain lead at the gas station pumps any more (although some independent stores do still sell Leaded Four Star Petrol).

Before unleaded petrol became available, all petrol contained lead as it lowered the octane level which prevents the fuel from igniting too soon.

However, lead is harmful to both humans and the environment so now it is banned in many countries including the USA and UK.

Unleaded vs Super Unleaded Petrol

As well as unleaded petrol, super unleaded (or the equivalent)  is now offered. 

However, it seems this only really makes a difference in high performance cars. It is better for3 these engines, and owners will notice a smoother ride as well as more miles to the gallon.)

For anyone with a "lower performance" car, they will probably find that super unleaded fuel does offer a few more miles to the gallon, but as this fuel costs more, there is little financial gain in the end.