One method of increasing forest carbon stocks that is often discussed is increasing stocking levels on existing forested lands. However, estimates of the potential increases in forest carbon sequestration as a result of increased stocking levels are not readily available. Using the USDA Forest Service's Forest Inventory and Analysis data coupled with the Forest Vegetation Simulator, we estimate that, for a seven-state region in the northeastern United States, timberland contains about 1768 Tg of carbon in aboveground live biomass across all stocking classes. If all medium and understocked stands had the carbon density of fully stocked stands, an additional 453 Tg of carbon would be stored. While the carbon gains per unit area are greatest for understocked stands, generally fewer than 10% of stands are in this condition. The increase in carbon storage per unit area is smaller for stands in the medium stocked class, but the large proportion of stands in this condition offers considerable opportunities. Our analysis indicates that, when seeking to increase forest carbon storage, managing stocking levels is an option with considerable potential, especially since no changes in land use are required.