I recommend a high quality fuel with additives aleady in the fuel. Not all fuels have this. Google "top tier gasoline" and review the entries there. If you want to use cheaper fuel, then you will need and benefit from fuel additives. As to oil additives, there are many additives on the market and I am not aware of one that is recommended by qualified independent petroleum engineers. Most if not all of these are simply not worth it. Use a top-quality synthetic like Mobil 1, and change it every 7500 miles or so. X5's and all BMW's may also benefit from higher viscosities than BMW recommends. One factor in BMW's recommendation is meeting CAFE standards, and a lighter weight oil helps achieve that, but possibly at some cost to valve train wear, especially in more severe conditions.