Crude oil cannot be used directly and must go through refining. At refineries, it is separated into petrol, diesel, kerosene and other products using processes like fractional distillation and catalytic cracking. On average, 1 litre of crude oil produces around 0.4 to 0.6 litres of petrol and 0.2 to 0.3 litres of diesel, along with other usable products.