In the third part of this series, we introduce the mathematical model for the agglomeration of gas hydrates in oil-continuous flow. The aim is to develop an expression for the agglomeration efficiency that considers the existence of wet or dry particles. If the particle is wet, then water is available at its outer surface, thus allowing the formation of a liquid bridge that holds the aggregate together. The criterion for a wet or dry particle was developed in part II of this series and arises from competitions between water permeation through the porous hydrate particle and water consumption caused by crystallization in the particle’s outer surface. The new expression for the agglomeration efficiency is coupled with a population balance solved through the method of moments and considering simple expressions for the collision rate and the shear rate induced by the flow arising from Smoluchowski’s and Kolmogorov’s theory, respectively. When compared to experimental data, the model stays within the ±40% deviation range and proves capable of predicting smaller agglomerate sizes for higher subcooling and lower interfacial properties (use of surfactant additives). The influence of subcooling on changing the porous medium parameters (especially the porous medium interconnectivity) proved important for the determination of the time taken for the particle to dry out. The model is simplified for engineering purposes considering gases much more soluble in oil than in water (hydrocarbon gases) in oil-continuous flow, and a simple criterion is proposed to predict if the system behaves as dispersed (slurry) or if it agglomerates after the onset of hydrate formation.