Abstract The preparation and inversion of relatively large droplet Athabasca Bitumen-in-water emulsions have been examined experimentally, The emulsions were prepared using small quantities of NaOH, followed by cooling to 20 ° C. Droplet size distributions were determined as functions of time, additive concentration, shearing rate, temperature and Bitumen concentration. The tests showed thot the droplet sizes increased continuously with time until failure or inversion occurred. For some emulsions, resistance to inversion could be improved by small quantities of a nonionic stabilizer. Introduction Heavy oil and Bitumen comprise a large proportion of the total Canadian petroleum resources whose importance continues to increase. Part of this increase is due to declining reserves of light crude but improvements in production and extraction technologies have also played a role. Transportation of Heavy oil from well to battery continues to be dominated by trucking but the combination of relatively high costs and environmental concerns has led to a search for alternative modes. One of these alternatives is emulsion pipelining. In an emulsion pipeline, the high viscosity (typically 100 poise) of the oil is relatively unimportant because shear occurs only in the low viscosity (1 centipoise) aqueous phase. The oil droplets increase the viscosity of the mixture to approximately I poise at a volume fraction of 0.7 but the energy consumptions remain modest as long as the pipeline flows are turbulent. A surfactant is required to form the desired oil-in-water or oil-in-brine emulsion at the oil concentrations required for economic pipeline operation. In most of the previous studies, e.g. references I and 2, emulsions with small (less than 10 microns) drops have been prepared. These ‘stable’ emulsions cream slowly and can be redispersed by stirring after standing for very long periods of time. If only short distance transport is required, stability is less critical and larger (above] 00 microns) droplet sizes can be used. The effective viscosities of these large-droplet emulsions is often lower than those of emulsions with fine droplets. Separation of the oil from the water at the pipeline outlet is easier and the quantity of surfactant required to prepare the emulsion is lower than for the ‘stable’ emulsions. However the role of the surfactant remains critical. Use of an unsuitable surfactant or an insufficient quantity of surfactant can lead to inversion to a water-in-oil emulsion. A water-in-oil emulsion would have a viscosity at least as high as the original oil. If this emulsion occupied the whole of the pipe cross-section for only a short distance, the pipe would be effectively blocked. The behaviour of a nonionic surfactant in large droplet Heavy oil-in-brine emulsions has been examined recently3 using laboratory bench tests, viscometry, particle size analyzer, a toroid pipe flow simulator and High Performance Liquid Chromatography. These experiments showed that the droplet size increases continuously and the surfactant concentration in the aqueous phase decreases during shearing or flow. At inversion, the droplet size rises drastically and the surfactant concentration falls to zero.