Oilfield operations such as drilling, reservoir management, and production require the injection and/or production of complex fluids to improve the extraction of crude oils. Some of these complex fluids such as drilling muds, fracking fluids, foams, emulsions, surfactants, and polymers, fall under the classification of colloidal suspensions which is one substance of microscopically dispersed insoluble particles suspended throughout another substance. These colloidal suspensions show complex rheological properties that are dependent on the suspension properties, flow conditions, and flow conduit dimensions. Rheology of colloidal suspensions is a complex subject that is still being investigated. The focus of this study is on heavy oil-in-water emulsions. Heavy oil and bitumen resources account for approximately 70% of the remaining oil discovered to date in the world. Heavy crude oils are costly to produce, transport, and refine compared to light crude oils due to the high viscosity of heavy crude oils. To improve the economic viability of producing heavy oils, especially in a time with low crude oil prices, operational expenses must be reduced. One of the main areas to improve is the cost associated with transporting produced heavy oils from production wells to refineries. Currently, heavy oils are diluted with low viscosity diluents such as condensates and light crude oils to lower the mixture viscosity below 350 cSt before heavy oils can be transported through pipelines. The diluted mixtures require up to 50% (vol.) diluents to lower the heavy oil viscosity. High demand and low supply of condensates and constrained pipeline capacities have resulted in pipeline transportation costs of up to 22/bblofdilutedheavyoilfromCanadatorefineriesintheU.S.Analternativemethodoftransportingheavyoilsistotransportheavyoilsinanemulsifiedform,heavyoil−in−wateremulsions,whichcanshowordersofmagnitudelowerviscositiescomparedtotheviscosityofheavyoils.Inthisstudy,asimple,one−stepmethodofpreparingheavyoil−in−wateremulsionswasdeveloped.Thephysicalpropertiesofheavyoil−in−wateremulsionsarecontrolledandmodifiedbyoptimizingthechemicalformulationusedtoprepareemulsions.Stableheavyoil−in−wateremulsionscanbepreparedwithchemicalformulationsthataretailoredtothetypeofheavyoilsandavailablewatersourceswhichcanrangefromfreshwatertosoftenedseawater.Therheologyofheavyoil−in−wateremulsionshasbeencharacterizedwitharotationalviscometer.Heavyoil−in−wateremulsions,especiallyconcentratedemulsions,showedcomplexrheologicalpropertiessuchasshearthinningbehavior,two−stepyieldstresses,two−stepwallslips,andrheopexy.Arheologicalequationandawallslipequationhavebeendevelopedtomodeltherheologyofheavyoil−in−wateremulsionsoverarangeofshearratesandflowconduitdimensions.Heavyoil−in−wateremulsionscharacterizedwithcapillarytubeviscometersshoweddrasticallydifferentviscositymeasurementscomparedtotheviscositymeasurementsobtainedwitharotationalviscometer.Thisisimportantbecausetheflowofemulsionsinpipelinesaresimilartotheflowofemulsionsincapillarytubeviscometers,notrotationalviscometers.ThelowerviscositiesmeasuredwithcapillarytubeviscometersareattributedtooildropletmigrationawayfromthetubewallsduetotheshearheterogeneityobservedinPoiseuille(tube)flow.Ascalingequationwasproposedtorelatetheviscositymeasurementsofemulsionswitharotationviscometertotheviscositymeasurementsofemulsionswithcapillarytubeviscometers.Therheologicalmeasurementsofheavyoil−in−wateremulsionsareusedtoestimatetheflowofemulsionsincrudeoilpipelineswithvariousradii.Viscositymeasurementsofoptimizedheavyoil−in−wateremulsionswitharotationalviscometershowedthatheavyoil−in−wateremulsionswithupto751-3/bbl of emulsion. Heavy oil-in-water emulsions also showed drag reduction properties which can significantly increase the maximum flow capacity of crude oil pipelines. Transporting heavy oils as concentrated heavy oil-in-water emulsions appeared to be a competitive if not a better method of lowering heavy oil viscosity compared to the diluent method in terms of cost and flow performance in pipelines.Petroleum and Geosystems Engineerin