A number of research groups have investigated the formation and stabilization of water-in-oil emulsions. A variety of compounds and mixtures have been shown to promote and stabilize these emulsions, including sea mater particulates, as well as fractions or compounds found in crude oil. Asphaltenes, resins and waxes in crude oil contribute to the formation of stable oil-in-water emulsions. Within the asphaltene fraction, the nickel porphyrins appear to play an essential role in emulsion formation. The vanadium porphyrins, although more abundant than nickel porphyrins in most crude oils, do not play an important role in emulsion formation, possibly because of their higher polarity. It appears that compounds with higher solubility in the oil phase than in the aqueous phase are the emulsifying agents that can promote stable water-in-oil emulsions. Crude oils that form very unstable emulsions, e.g. Gullfaks crude oil from the North Sea, require weathering as well as the addition of nickel porphyrins before a stable emulsion will form. The weathering may cause the formation of colloidal asphaltene particles and highly polar compounds that contributes to emulsion stabilization. Essential to the formation of stable water-in-oil emulsions are sufficient amounts of certain polar compounds. If there are insufficient amounts of these compounds, then even the presence of particles and waxes will not lead to the formation of stable emulsions,