An essential part of using electrical geodiagnostic techniques to map thermal recovery processes is understanding the relationship between the process and the formation resistivity. This paper shows how the relationships used to interpret electrical well logs can be used to understand steamflood resistivity changes. Examples are presented of data from steamfloods in fields with different reservoir characteristics. Included is a typical heavy-oil steamflood (Kern River field) and a steamflood where fresh water is used for the steam generator feedwater (Elk Hills field). Because of differences in reservoir characteristics, changes in resistivity vary from reservoir to reservoir. The information presented include well logs taken before and after steamflooding and petrophysical measurements sufficient to determine the factors that controlled the resistivity changes in each field.