To choose the right type of oil for your engine, refer to the service documentation that came with the car from the manufacturer. The documentation recommends the viscosity range that the oil should fall in.
Another way of determining the right engine oil is using an online service, such as the one offered at Halfords.com. Enter either your car's registration number or its specifications, then search to see the recommended oils.
The four main types of engine oil you can choose from are premium conventional oil, full synthetic oil, synthetic blend oil and high-mileage oil. Premium conventional oil is the standard oil for new cars. It is available in many viscosities. Full synthetic oil is made specifically for cars with high-tech engines. Though long-lasting, you should only use it if the manufacturer recommends it because it may only be an added expense if your engine doesn't need it.
Synthetic blend oil is a mixture of synthetic oil and organic oil. Though more expensive than premium conventional oil, it's cheaper than full synthetic oil. High-mileage oil is made specifically for engines with high mileage. It is developed with seal conditioners, which not only increase the flexibility of seals but also restore their shape.