Factbox: Key facts about the Alaska Pipeline Project

(Reuters) - TransCanada Corp (TRP.TO) and Exxon Mobil Corp (XOM.N) started the process on Friday for signing up potential shippers for their massive Alaska natural gas pipeline to southern markets.

The companies also boosted the price tag for the proposed pipeline, which would run to the Alberta border in Canada from Alaska's North Slope, or under an alternative plan, to Valdez, on the state's southwestern coast.

Here are some facts about the Alaska Pipeline Project.

Point Thomson transmission line

Length: 58 miles

Diameter: 32 inches

Capacity: 1.1 billion cubic feet per day

Alberta case

Cost: $32 billion-$41 billion

Length: 1,700 miles

Diameter: 48 inches

Base capacity: 4.5 bcfd

Capacity (with max. compression): 5.9 bcfd

Valdez case

Cost: $20 billion-$26 billion

Length: 803 miles

Diameter: 48 inches

Base capacity: 3 bcfd

The open season to gauge interest in securing capacity among potential shippers runs May through July, 2010.

The proposed in-service date is around 2020, two years after previous target.

(Reporting by Jeffrey Jones; editing by Rob Wilson)