In oil production, co-produced water is mixed with the oil in choke valves and process equipment producing water-in-oil emulsions. The amount of water increases during the production life of the reservoir. The emulsions are destabilized using gravitational separators, and the settling rates are increased by applying heat, demulsifiers, and AC electric fields. The AC electric field gives rise to attractive forces between water droplets and increases the probability of coalescence at contact. According to Stokes law, the settling rate increases proportionally with the square of the drop diameter. By promoting coalescence of small water droplets, the settling rate can be greatly increased. The water content is normally reduced to <0.5 vol% if this is the final treatment stage before the crude oil is exported.