An oil sample is subjected to nuclear electromagnetic irradiation downhole, and the electron and/or mass density of the oil sample is determined by measuring the attenuation of the irradiation and relating the attenuation to the electron density. If the irradiation is high energy gamma ray irradiation, the attenuation is considered to be a function of Compton scattering only, which in turn is related to the electron density of the sample. If X-rays are utilized, attenuation is preferably measured in two energy windows. Using the two different attenuation values found in the different windows, the attenuation due to Compton scattering can be found and related to the electron and/or mass density of the sample. In addition, attenuation due to photoelectric absorption may also be determined and related to the presence of one or more heavy elements in the oil (e.g., sulfur) and/or sanding.