actually l am afraid of the petrol usage and of the maintenence,, l know it is very luxury car, some body has s500 can tell me?

Which one are you interested in? The '99 S500 was the last year of the W140 chassis and 2000 was the first year of the next generation W220 chassis S-Class.

Overall, l prefer the older W140 generation. It was the last of the ''tank'' models. It is a very solid platform and a great luxury cruiser. The next generation S-Class, while still a very nice vehicle, lacked that vault-like driving experience that the previous S-Class enjoyed.

I'd go with 2000 or later, because Mercedes had problems with transmission in some cars before 2000.
If you are worried about petrol usage, you might consider an S430, which is better on gas.

it can be GOOD CAR DEPENDS ON THE SERVICE HISTORY AND WHOM DID THE SRVICE AND HOW MUCH EXPERIANCE THAT PERSONE HAVE