Variation

 Different countries have different energy and pollution standards resulting in differences in composition. Petrol pumped out of the service station are mixed with other chemicals (such as detergents and even alcohols derived from sugarcane and other botanicals) to meet national standards and requirements.

petrol or gasoline is a mixture of several hydrocarbons with some detergents and additives -- for better engine performance, reduction of knocking etal.
The mix varies depending upon the composition of the original crude (crude oils from various sources have different compositions), refinery efficiency, price of various distillates in the market at the time, et al
National emission regulations also determine the nature and quanta of additives & detergents