1. For use in logging downhole in an earth borehole, a method for determining a characteristic of oil that may be present in a downhole measurement region, comprising the steps of: providing a plurality of crude oil samples; determining the viscosities of the crude oil samples; performing test measurements, using a predetermined operating mode, on media including said crude oil samples to obtain test data; applying a test processing procedure to said test data to obtain an output test parameter relating to said test data and said predetermined operating mode; deriving, for said plurality of crude oil samples, a correlation relating said output test parameter to the viscosities of said crude oil samples; performing downhole measurements in the measurement region with a logging device, operated with substantially said predetermined operating mode, to obtain logging data, and applying a measurement processing procedure to said logging data to obtain an output logging parameter; and determining the oil characteristic using said output logging parameter and said correlation.