Origin and Destination: The reversal involves Enbridge’s existing Line 9, which currently transports crude oil from Montreal, Quebec to Sarnia, Ontario. With the reversal, oil would instead flow from Sarnia to Montreal. Through the Portland-Montreal Pipe Line (see below), it could then flow to Portland, Maine, where it could be shipped along the Gulf Coast via tankers. The proposal was seen as opening a gateway for oil sands to travel to the Atlantic Coast for the first time.

Length: 524 miles

Capacity: A minimum of 50,000 barrels per day of crude oil through the Trailbreaker, with a maximum capacity of up to 200,000 barrels per day

Cost: $346 million

Project status: The project was put on hold in 2009 due to lack of commercial support. Enbridge says it is no longer pursuing the project, but the company has asked the National Energy Board in Canada to allow for a partial reversal of Line 9. Conservationists say that is evidence that the company is now trying to accomplish its goals through piecemeal reversals on the line.

Montreal Pipe Line Ltd

Company building it: Montreal Pipe Line Ltd

Project date: Project conceived in 2008. On hold.

Origin and Destination: The project would reverse a Portland-to-Montreal pipeline that has been in place since 1941, and complete the final leg of the Trailbreaker project to the Atlantic.

Length: 236 miles

Capacity: Approximately 400,000 barrels per day

Cost: The reversal would require $100 million in modifications.

Project status: In February 2012, the Court of Quebec rejected Montreal Pipe Line Ltd's request to construct a pumping station near the Quebec-Vermont border, a crucial piece of the company’s plan to reverse the flow direction of its pipeline. On March 21, Montreal Pipe Line announced that it would not appeal the court's ruling. "At this point in time, we do not have an active project due to economic and market conditions," said Larry Wilson, the company's president, in a press release.

InsideClimate News intern Zoe Schlanger contributed research to this report.