The flow of a commodity is modelled as a quasi-thermodynamic irreversible process. The flow is treated not as a mass quantity, but more like a transient energy quantity. A commodity is thus considered an artefact that depends on whether it resides or is stored within the system or is in transit across the system boundary to the surroundings. This allows the use of the fundamental laws of thermodynamics and brings further insight into the process of commodity diffusion. The methods of irreversible thermodynamics are also considered and a coupling relationship between commodity price and quality is derived.