General Northern Gas Pipeline-related News From Canada Reuters.  Exxon Mobil Corp (XOM.N) continues to work on advancing the C$16.2 billion ($15 billion) Mackenzie Valley gas pipeline, a senior executive of the U.S. major said on Friday.  Andrew Swiger, senior vice-president at the world's largest publicly traded oil company, said at a Calgary presentation that the company, one of five partners in the planned line to carry natural gas from the Canadian Arctic to southern markets, is still advancing the project.     *     Imperial Oil profit sags on low prices, [...]