Kinder Morgan has shut down a pipeline that runs from Alberta to the West Coast while it investigates a possible oil leak.

The Trans Mountain pipeline was shut down on Friday afternoon as a precaution after a small amount of crude was found on a farmer's field about 150 kilometres west of Edmonton, company spokeswoman Lexa Hobenshield said Monday.

"We are investigating whether the product is from a current release or historic incident," she said in an emailed statement.

She added it's not yet clear exactly how much crude spilled, or when the 300,000-barrel-per-day system may be up and running again.

The Trans Mountain line stretches 1,150 kilometres between Edmonton and terminals in the Vancouver area and Washington State. It carries heavy and light crude oil, as well as refined products such as gasoline and diesel.

Houston-based Kinder Morgan owns or operates nearly 60,000 kilometres of pipelines and 180 terminals in North America.

Calgary-based Enbridge Inc. is planning to build another pipeline from the Edmonton area to the West Coast, called Northern Gateway.

That controversial line would wind up much further north on the coast than Trans Mountain, to connect with the port of Kitimat, B.C.

The crude would then make its way to Asian markets by tanker.

Enbridge grappled with two high-profile pipeline leaks in the U.S. Midwest last summer. Outages on those lines caused major bottlenecks for Canadian crude that was bound for U.S. markets.