Before revision: In the EU , it is not illegal for a person or business to buy fuel in one EU state for their own use in another, but as with other goods the tax will generally be payable by the final customer at the physical place of making the purchase.
After revision: Within the European single market , it is legal for a person or business to buy fuel in one EU state for use in a vehicle in another, as well as a small amount of fuel in a container, but as with other goods , taxes (such as VAT) will generally be payable by the final customer at the physical place of making the purchase.