To enhance the more than 1.4 million miles of pipelines, natural gas is stored in two basic ways – compressed in tanks as liquified natural gas (LNG) or in large underground storage facilities such as depleted gas wells, salt caverns, or rock caverns, abandoned mines, and aquifers. By far, the greatest volume of gas is stored by this second method, usually in depleted gas wells. Each year, from April to November, operators inject excess summer production into approximately 415 storage reservoirs across the country. Most of these facilities are located near major eastern and mid-continent markets. They account for almost 4 trillion cubic feet of storage capacity, or over 15% of one year's national gas consumption. This storage system serves the market place in several ways. Most importantly, it allows consistent delivery of the natural gas resource to consumers. Second, it stabilizes supply by sustaining production levels in the summer and eliminating shortages in the winter. Third, it eliminates the need for expensive, additional pipeline transmission capacity that would be necessary to supply peak demand. Finally, it provides confidence in and encourages the use of an environmentally friendly, clean burning fossil fuel.