Car, what oil?

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A fairly new driver here, got a second hand car. Doing the checks on it and I need oil for it.
I've checked online for my car but sites are giving me two different types of oil. Eg, 5w30 vs 10w40. How do I know which one is correct? Thanks

Do you have an owners manual? It should be in there, otherwise you will need to look on a website like eurocarparts.com, enter your registration number, check that it finds the make and model of your car, go to service items, and you will see oil. In there you will see all the compatible oils for your car.

Never needed to top up the oil on any of my cars. Is there a leak? Has it been maintained properly?

Just take it to your local garage for an oil change and they will put the right oil in. I do an oil change before every MOT and my cars have galactic scale mileage on them.

If you go to Halfords and give them your reg they will tell you

Put your number plate in here

Many cars use some oil between services. The OP doesn’t need an oil change unless it’s due. Other posters have already posted sensible links to find the correct oil but there’s also this www.castrol.com/en_gb/united-kingdom/home/product-finder.html