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Savant Technical Consulting has conducted a review of literature that have used carbon “stock and flow approaches” to evaluate biofuels, bioenergy, and bioproducts. These stock and flow approaches have been compared to attributional and consequential life cycle assessment methods. We have used the term “stock and flow approaches” to capture the diverse forms of stock and flow models, which can differ materially in terms of complexity, scope, and boundary conditions. Stock and flow approaches aim to track the amount of carbon present in different pools within the ecosphere, and the exchange of carbon between these pools. The key pools include the atmosphere, soil, water, and land. Each of these may be divided into sub-pools that capture different spatial or compositional features, e.g., different ocean or soil depth, or different types of biomass on land. Earth system models (ESMs) represent the most comprehensive type of stock and flow model for carbon. ESMs have massive data requirements, and large uncertainty in model parameters, but represent the gold standard for tracking carbon through all major pools. Simplified stock and flow models have been developed for biofuels, bioenergy, and forest products, which can materially reduce data requirements and computational complexity. These simplified stock and flow models generally exclude certain pools (e.g., soil, or water), and may have narrower system boundaries (e.g., a regional forest or agricultural area, rather than the whole Earth). These simplifications lead to an issue with carbon “leakage” across the system boundaries. Such leakage (or “missing carbon”) must be quantified in order to properly interpret results from a simplified stock and flow model.