The diesel price in Belgium is rising and at this moment 4,5 cents p/l higher priced than the Dutch retail price. Nevertheless, it pays off for companies to fuel up in Belgium, due to the high fuel excise rebate which is currently 21,33 cents per liter. 

This is a rebate especially for transport companies with trucks weighing more than 7.500 kilograms. With this rebate you will still have an advantage of at least 16 cent per liter. Because the private sector does not benefit from this, you could find the Belgian refuelling more often in the Netherlands.