Stock models are useful for quantifying geothermal resources with a focus on important large-scale reservoir characteristics such as energy content, well deliverability and recharge into geothermal systems. Stock models have the benefit of being dynamic, although they do not require much more input than the volumetric models used commonly in the geothermal industry. Stock models can also be calibrated to production histories from geothermal systems in various settings and at varying stages of development. Due to its simplicity, the stock modelling method lends itself well to statistical methods, strategic optimization and integration with financial models.