Conventional mineral Oil: This is the standard new-car oil. All leading brands have one for service level SL, available in several viscosities. The car makers usually specify a 5W-20 or 5W-30 15w-40W oil, particularly for lower temperatures, with a 10W-30 oil as optional, particularly for higher ambient temperatures. These four ratings cover just about every light-duty and many trucks and HGV’S vehicle on the road. Even more important, though, is changing the oil and filter regularly. A 4000 miles/4 months interval is good practice. The absolute minimum is twice a year. If your car has an electronic oil-change indicator on the instrument cluster, don't exceed its warning. Semi-Synthetic Oil: These have a dose of synthetic oil mixed with mineral oil, and overall are formulated to provide protection for somewhat heavier loads and high temperatures. This generally means they're less volatile, so they evaporate far less, which reduces oil loss (and increases fuel economy).  they're a lot less expensive than full synthetics, maybe just pennies more than a premium conventional oil Full Synthetic Oil: The oils made for high-tech engines, whether in a Ford or Mercedes-Benz, are full synthetics. If these oils pass stringent special tests, it means they have superior, longer-lasting performance in all the critical areas, from viscosity index to protection against deposits. They flow better at low temperatures and maintain peak lubricity at high temperatures. Higher Mileage Oil: Today's vehicles last much longer and older classics, you have another oil choice, those formulated for higher-mileage vehicles. Almost two-thirds of the vehicles on the road have more than 75,000 miles on the odometer. So the oil refiners have identified this as an area of customer interest, and have new oils they're recommending for these vehicles. When your car is somewhat older and has considerably more mileage, you may notice a few oil stains on the garage floor. It's about this time that you need to add oil more often than when the vehicle was new. Crankshaft seals may have hardened and lost their flexibility, so they leak (particularly at low temperatures) and may crack. The higher-mileage oils are formulated with seal conditioners that flow into the pores of the seals to restore their shape and increase their flexibility. In most cases, rubber seals are designed to swell just enough to stop leaks. But the oil refiners pick their "re swelling" ingredients carefully.. You also may have noticed some loss of performance and engine smoothness as a result of engine wear on your higher-mileage vehicle. These higher-mileage oils also have somewhat higher viscosities. (Even if the numbers on the container don't indicate it, there's a fairly wide range for each viscosity rating and the higher-mileage oils sit at the top of each range.) They also may have more viscosity-index improvers in them. The result? They seal piston-to-cylinder clearances better, and won't squeeze out as readily from the larger engine bearing clearances. They also may have a higher dose of antiwear additives to try to slow the wear process