[6] The expansion, which runs roughly parallel to the existing pipeline, increased capacity from 300,000 to 890,000 barrels per day (48,000–141,000 m3/d), at a cost of C$53 billion.

A Supreme Court decision on July 2, 2020, that rejected the appeals made by First Nations and environmental groups, "[brought] an end to the years-long legal challenge".

[8] On August 31, 2018, the Government of Canada purchased the pipeline for $4.7 billion[9] from Kinder Morgan through the creation of the Trans Mountain Corporation (TMC), in order to "keep the project alive".

The idea for a pipeline from Alberta to British Columbia quickly emerged, driven by the growing demand for oil both in Asia and on the west coast of Canada and the United States.

The governments considered the TMPL to be a strategic way of reducing reliance on oil tankers, made vulnerable under threats of potential attack on the west coast of North America.

[clarification needed] In August 1953, crude oil from Edmonton, Alberta, began flowing to refineries in the Vancouver area and the northwestern U.S. through TMPL.

[1] A 1993 report said that the TMPL was the "only major system in the world" at that time, transporting both crude oil and refined petroleum products" in a single pipeline.

[17][1] By 1998, TMPL made regular shipments to Vancouver of refined petroleum products "including jet fuel, gasoline (unleaded and premium unleaded), diesel (regular sulfur, low sulfur, and low temperature), methyl tertiary butyl ether (MTBE), and crude-oil (light sweet, light sour, and heavy)".

[18] According to a 2016 Oil Sands Magazine article, this resulted in the conversion of existing refineries along the TMPL route into storage and distribution facilities and terminals.

Premier Christy Clark announced British Columbia's support for the expansion of the Trans Mountain pipeline, saying the project met her government's five conditions for approval and included a revenue-sharing agreement worth up to $1 billion.

[41] On January 3, 2024, Trans Mountain Corp said in a 33-page filing that it planned to begin line fill in March or May, depending on the diameter of pipe to be used and assuming no new problems.

The project nearly tripled oil pipeline capacity from Alberta to Canada's Pacific coast to 890,000 barrels per day (141,000 m3/d), enabling better access to global markets and boosting crude prices.

To reach the terminus, tankers have to pass through a very narrow channel of shallow water from the open sea, still putting leaks at risk due to vehicle crashes.

government proposed a restriction on increases to the amount of diluted bitumen that could be imported into the province from Alberta, until the completion of studies on whether potential spillage could be mitigated.

On February 6, 2018, Notley ordered the Alberta Gaming and Liquor Commission to cease future imports of British Columbia wine as a retaliatory sanction over these moves.

[57] On April 8, 2018, Kinder Morgan suspended "non-essential" activities relating to the pipeline, as the company did not want to "put [its] shareholders at risk on the remaining project spend".

Attorney General David Eby threatened to sue Alberta over the act, as he considered it unconstitutional, and stated that it could have a further impact on gasoline prices in the province.

The government did not intend to remain the permanent owner of the pipeline, as it planned to seek outside investors to finance the twinning project.

[65] However, the same day, the Federal Court of Appeal overturned the government's approval of the expansion project, citing that it did not sufficiently fulfill its constitutional duties to consult local First Nations groups,[66][67] and because it lacked an environmental assessment of increased tanker traffic on orcas in the Salish Sea[68] off the BC coast.

[39] Members of the Squamish and Tsleil-Waututh in British Columbia paddled canoes on Burrard Inlet, in North Vancouver, to Kinder Morgan's Burnaby Terminal for a ceremony to protest the expansion of the Trans Mountain pipeline.

Their claim is that the First Nation band governments only have jurisdiction through Canadian law on their reserves, whereas traditional Secwépemc leadership retains sovereignty over Secwepemcul’ecw.

[79] The establishment of the camp led Kúkpi7 (Chief) Rosanne Casimir of Tk’emlúps te Secwépemc First Nation (TteS), along with Chief Shelly Loring of Simpcw First Nation to issue a joint statement asking the Tiny House Warriors to stand down, claiming it was the Warriors violating Secwépemc law.

By October 15, the RCMP had begun arresting people connected to the camp, including Hereditary Chief Segwses, Loralie Dick, April Thomas, Billie Pierre and Romilly Cavanaugh.

[77] In a statement released the next day, TteS Kúkpi7 Rosanne Casimir thanked the RCMP for maintaining peace and order and stated that she and the elected council did not endorse the protesters.

[68] The hearings were also restricted by the NEB panel to investigate "new information" as it related to the impact of increased oil tanker traffic to and from the Westridge Marine Terminal in Burrard Inlet, Burnaby, to Canada's 12-nautical-mile territorial waters.

The environmental concern in this area included the Salish Sea's southern resident killer whales' (SRKW) prime Chinook salmon feeding ground.

[68] Noise and pollution from marine vessels along with the diminishing stocks of salmon – their prime source of food – contributed to the whales' declining numbers.

[68] Hearings in the form of pipeline roundtable meetings with Trans Mountain representative and indigenous groups were held in Calgary in November 2019 as well as in Kamloops and Nanaimo in December; the summary is expected in January 2020.

[85] Both the NEB and the federal government acknowledged that there was a possibility that TMX could "damage the environment and marine life", but the benefits outweighed the risks.

[85] Trudeau said that the revenue from TMC, which was estimated at $500 million annually just in federal corporate taxes, would be invested in "unspecified clean energy projects".