A first-ever friction-wear model for Four-Ball Extreme Pressure (EP) Lubrication is developed in this work based on 12 oil samples comprising minerals, esters and other formulated lubricants. The model considers the rate of entropy generation and dissipation within the lubricated tribosystem to describe the interaction between the friction and the wear behaviours at extreme pressure condition. The model can be used to calculate the probability to pass or fail at a specific load to estimate the weld point of a lubricant. The calculated probability exhibited similar trend as load-wear index from ASTM D2783 EP test method. Besides, the model is able to estimate the EP performance of an unknown lubricant based on the model parameter namely dissipative coefficient. This parameter describes the proportionality between the friction and the wear phenomena from the perspective of thermodynamic analysis. This work provide useful tools to better understand the fundamentals of EP lubrication and to characterize the lubricants without overly relying on tribotest machines.