Natural gas vehicle gas has the highest energy/carbon ratio of any fossil fuel, and thus produces less carbon dioxide per unit of energy. The major difficulty in the use of natural gas is transportation. Natural gas pipelines are economical and common on land and across medium-length stretches of water (like Langeled, Interconnector and Trans-Mediterranean Pipeline), but are impractical across large oceans. Liquefied natural gas (LNG) tanker ships, railway tankers, and tank trucks are also used. CNG is typically stored in steel or composite containers at high pressure (3000 to 4000 psi, or 205 to 275 bar). These containers are not typically temperature controlled,
Carbon capture and storage (timeline) Sleipner field produces natural gas and light oil from the Heimdal sandstones, which are about 2,500 m below sea level. The natural gas produced at Sleipner contains unusually high levels (about 9%) of carbon dioxide, but the customers require less than 2.5%. To encourage companies to cut their carbon emissions, the Norwegian government imposes a carbon tax equivalent to about $50 per ton of CO released into the atmosphere. To avoid paying the tax, and as a test of alternative technology, all of the CO extracted since 1996, when gas production started at Sleipner, has been pumped back deep underground.