What is the difference between diesel and gas fuel?

HI, The main difference is that a diesel engine uses compression to ignite its fuel, and a gas engine is the same as a petrol, it uses a spark to ignite its fuel. Diesel engines are more fuel efficient than petrol or gas. For instance if a diesel used 10 liters per 100kms a petrol engine of the same size in the same car would use roughly 12 liters per 100kms and a gas engine 15 liters per 100kms. Diesel engines are more ruggedly built to withstand the shocks and forces produced by compression ignition and therefore will generally last longer. Gas though, is the cheapest fuel on the Australian market so it is the cheapest to run in fuel cost. Personally I'm a diesel mechanic so i would say diesels are better, but if your after short term savings on the fuel bill I would go for a gas engine