In essence, the workers' compensation system in place in the United States is actually a network of state-level private insurance systems, each of which is governed by similar but distinct state laws. Most companies opt to purchase workers' compensation insurance policies from third-party carriers, exchanging the payment of premiums for offloading some of the risk they bear. However, some large companies may choose to self-insure, taking on the financial responsibility for their own workers' compensation claims. The system that is used to determine insurance premiums is based on workers' compensation classifications, which rank each sector according to relative risk of injury and accidents. The most prevalent classification system used to set rates is devised and maintained by the National Council on Compensation Insurance, an advisory organization with no regulatory or enforcement powers. However, several states have opted not to use the NCCI classification system and rely on other methods to set workers' compensation insurance rates.