This paper presents the first part of an experimental study performed jointly by IFP and Saudi Aramco to characterize the stability of emulsion samples collected from different Saudi Aramco Gas/Oil Separation Plants (GOSP). Earlier studies1-2 have shown the importance of emulsion characteristics on the performance and optimization of oil-water separation at Saudi Aramco GOSPs. A strict and rigorous methodology was applied to understand the characteristics, behaviour and composition of these systems. Samples were first separated by simple gravity sedimentation in order to identify the amount of separated water, oil and residual emulsion. Each separated phase was then analyzed separately. This included the chemical composition and bulk properties of crude oil and the salinity of the separated water phase. Residual emulsions were characterized using several techniques including Karl Fisher analysis for water content, as well as optical microscopy, DSC (Differential Scanning Calorimetry) and cryo-SEM to assess the size and polydispersity of the dispersed droplets. The objective of the study is to highlight the main physico-chemical parameters responsible for the varying tightness of these emulsions, and provide insights to optimize their treatment costs and resolve emulsion issues in the GOSPs. The second part of this study still under progress will investigate the stability of residual emulsions in terms of chemical demulsification and interfacial properties.