JUNEAU, Alaska — Two of the world's largest oil companies announced plans today to jointly develop a multibillion-dollar natural gas pipeline to move North Slope natural gas to market.

BP and ConocoPhillips said in a joint statement that they plan to spend $600 million to reach the first major project milestone, an open season, commencing before the end of 2010.

The two companies have assigned staff on the project, expected to be the largest construction project ever in North America.

Gov. Sarah Palin had earlier rejected the proposal by ConocoPhillips to build a natural gas pipeline linking the state's energy rich North Slope to Midwestern states, opting to stick with a plan by pipeline company TransCanada. That company's plan for a pipeline remains under review.