Gas hydrates are ice-like solids that can form in crude oil flowlines at high pressure and low temperature; in severe cases, hydrate particles may aggregate in the oil phase and ultimately occlude flow in the line. In order to quantify the risk of plug formation, an accurate universal predictive model for hydrate-in-oil slurries is required. Currently, only one model has been proposed to predict the viscosity of hydrate-in-oil slurries, with an average deviation of 70% from new experimental data. In this work, a temperature-controlled, high-pressure rheometer with a vane blade rotor was deployed to study the rheological properties of hydrate-in-crude oil slurries, which were reacted from water-in-oil emulsions with and without anti-agglomerants (AAs). The results indicate that the addition of AA greatly reduced the viscosity of the hydrate-in-oil slurry, while the slurry maintained shear thinning behavior. The infinite shear viscosity data showed the basis of the current hydrate slurry model is does not appropriately capture the rheological properties of hydrate suspensions. By considering the shape effect of hydrate particles, a new model for hydrate-in-oil slurry has been proposed.