Open-access Resource
In resource economics, an open-access resource is one from which no potential user can be excluded. The category is often confused with a 'commons,' but a true commons typically has rules limiting who may use it and how — a distinction central to Elinor Ostrom's critique of Hardin.
An open-access resource is a natural resource or shared facility from which excludability is absent: no individual or institution can effectively prevent others from using it. Classic examples include the high seas before modern fisheries treaties, the atmosphere as a sink for greenhouse gas emissions, and groundwater aquifers with no extraction controls. Open-access resources are vulnerable to the dynamic described in the Tragedy of the Commons: because each user captures the full benefit of additional use while the cost of depletion is shared, total use tends to exceed the resource's carrying capacity. Economists distinguish this case from common-pool resources that are formally or informally managed — a distinction sharpened by Elinor Ostrom, who argued that Garrett Hardin had conflated the two. A regulated village pasture or a community-managed fishery is not open-access even though the resource is shared, because membership and use are constrained by rules. The standard policy responses to genuine open-access problems include privatization (assigning property rights), state regulation (quotas, licensing, taxes such as a Pigouvian tax), and the creation of community or co-management institutions in the style Ostrom documented. Which response fits depends on the physical nature of the resource, the user community, and the available enforcement infrastructure.