If you are abroad in a spanish-speaking country and you need to tell someone that you want to rent a car you must say:
-Quiero alquilar un coche
(I want to rent a car)
In Latin America you should change the word 'coche' (car) only used in Spain and replace it for 'auto' or 'carro'.
If you need an insurance as well you must ask:
'Puedo contratar un seguro?'
(Can I get an insurance?)
In case you want a diesel car you would have to say:-'Quiero un coche diesel'
(I want a diesel car)
-Este coche is gasolina o diesel? (This car is petrol or diesel?)
Words for petrol and diesel are also different in some coutries:
Petrol: Gasolina (Spain), Benzina (Chile), Nafta (Argenttina)
Disesel: Gasoil/Diesel (Spain), Gasoleo/Diesel (Latin America)