Energy companies and governments are struggling to advance multibillion-dollar pipelines to tap Arctic gas reserves and bring the supplies to North American markets. Here are the proposals.

MACKENZIE GAS PROJECT

Partners: Imperial Oil Ltd, Royal Dutch Shell, ConocoPhillips, Exxon Mobil Corp, Aboriginal Pipeline Group

Estimated Cost: C$16.2 billion ($15.3 billion)

Route: would extend through the Northwest Territories to TransCanada Corp's Alberta pipeline network from the Mackenzie Delta near the Beaufort Sea Coast, a distance of 1,220 km (760 miles).

Supply: three anchor fields in the delta, all discovered in the early 1970s, would initially supply up to 1.2 billion cubic feet a day. Reserves are currently estimated at 6 trillion cubic feet. Could support future onshore and offshore production.

Timetable: The partners filed applications in 2004, targeting a start to operations in 2009. Now, Joint Review Panel expected to deliver report on environmental and socioeconomic impact in December. National Energy Board to hear final arguments in April 2010.

Hurdles: Ottawa and project proponents still negotiating a package of government fiscal support measures. Unclear if the partners still believe the line would be profitable given uncertain outlook for gas markets. Momentum for an Alaska pipeline could move it ahead quicker and take away steel and skilled labor.

ALASKA PIPELINE PROJECT

Partners: TransCanada Corp, Exxon Mobil

Estimated Cost: at least $26 billion

Route: would extend through Alaska, Yukon and British Columbia to Alberta border from the North Slope, a distance of 2,737 km (1,700 miles).

Supply: line would initially ship 4.5 bcf a day from recoverable reserves on the Alaska North Slope that are estimated at 35 tcf.

Timetable: TransCanada plans open season to gauge shipper support in summer 2010, regulatory applications in 2012, possible project sanction in 2014, in service 2018.

Hurdles: Project has the support of the state of Alaska, giving it access to $500 million in public funding, but not the backing of two of the three North Slope gas producers, which are planning their own project (see below). Regulatory processes in two countries could be complex and expensive.

DENALI

Partners: BP Plc, ConocoPhillips

Estimated Cost: $30 billion

Route: Similar to the Alaska Pipeline Project to Alberta from the North Slope, but may also include another 2,400 km (1,500 mile) extension to Chicago.

Supply: Same reserves as Alaska Pipeline project, capacity of 4 bcf a day.

Timetable: Partners plan an open season to gauge support for the project before the end of 2010. Start-up is currently planned for 2018.

Hurdles: The project is being planned outside the state's Alaska Gasline Inducement Act, which leaves it without public funding. Partners do not have the support of Exxon Mobil, so the level of financial commitment needed from an open season is unclear. Project does not have agreement interconnect with TransCanada's Alberta system, which offers access to numerous North American markets. Sources: Company reports, U.S. Dept. of Energy

(Reporting by Jeffrey Jones, editing by Claudia Parsons)

Energy Conocophillips