I will be sharing the kind of Oil I use in my Car. And Why. I am not an expert in engine oils, however I have always been very particular about the type of Oil in put into my car. Before that - a brief about my daily driver. I currently drive a BMW X3 2011(F25 Chassis). I bought it Tokunbo and I have been driving it for over a year. It's a high mileage car - 260k KM on it. I am not aware of its previous owners maintenance history. However the engine runs smooth and I intend to keep it that way. Back to the discussion. Given the age of the car and its high mileage. I decided to be more careful with the type and spec of oil I put into the car. Unfortunately in this part of the world (Nigeria). We rarely care about stuffs like this. Most people assume just putting in any oil will okay. Unfortunately, they end up contributing to the early retirement of their engines sooner than it should have been. I went for an oil change and the guy at the filling station oil changing station said I should go for a specific brand that thats what other car users are putting into their cars and it doesn't give issues - he was pointing to a Toyota. In my mind I was like, this guy has no idea that engines are not the same or even spec'd the same by manufacturers. I told him "thanks for your input" and went in to the adjoining store in the Station to get 0w-40 (synthetic mobil 1 oil). Reason. 1. The "40" in the 0w-40 means the synthetic oil gets thicker when the engine runs hot. I live in the northern Nigeria - Kaduna. Using a lower spec'd oil, say Xw-20 has low viscosity (layman terms - how slow the oil flows from one point to another) of the oil will be too light and will be too thin to achieve good lubrication of the engine parts and that will invariably cause engine parts to wear off faster. All engine parts ever so slowly scrap against each other and tiny micro metal fragments starts to shear off your engine parts which may lead to lower tolerances (layman terms - microscopic gaps that causes vibrations and tiny movements in joints) inside your engine. 2. The "0w" is for cold environments in temperate regions. We are not really bothered about this.. as our climate in Nigeria is usually above 25 degrees. A morning cold start in Nigeria interacts just fine with most oils with our climate in Nigeria. 3. If you travel or go on long trips, the high viscosity saves your engine by protecting parts over sustained high temperature trips.