Toyota Prado: Which oil should I use?

I HAVE HAD a 2002 Toyota Prado turbo-diesel auto since new and have been doing oil changes every 5000km between the 10,000km scheduled services. What confuses me is the different engine oils on offer. Most claim to be suitable for diesel engines (as stated on the labels). I have always bought diesel engine oil as I thought diesel and petrol engines need different types of oil. I wonder what kind of oil the dealer used for servicing my car. I believe they use only one cheap standard oil for all oil changes on all cars.