HOUSTON – A price war is brewing between Canada and Latin America over who will satisfy U.S. Gulf Coast refiners' hunger for heavy oil.

The new Seaway Twin pipeline will almost double the amount of heavy Canadian crude coming to Gulf terminals and plants to about 400,000 barrels a day starting in January, according to Calgary-based ARC Financial Corp. The shipments are growing even without the Keystone XL pipeline, which has been delayed for six years because of environmental opposition.

The Canadian supply will square off against crudes from Mexico and Venezuela that have traditionally fed refineries along the Texas and Louisiana coasts. State-owned Petroleos Mexicanos widened its discount for U.S. buyers in December by the most since August 2013. Valero Energy and Marathon Petroleum, which invested in special equipment to refine heavy crude, stand to gain the most from the Canadian supply.

"Something's going to have to give," said Ed Morse, Citibank's head of global commodities research in New York. "It's going to have to be combination of Latin American countries exporting less into the U.S. or Canadian crude being re-exported and competing with crudes in other markets, particularly Europe."

New pipelines and rail terminals enabled more Canadian oil to head south to higher-value markets, partly offsetting a 48 percent collapse in global prices since June as the Organization of Petroleum Exporting Countries refused to cut production to counter a global glut.

The discount of Western Canadian Select priced in Hardisty, Alberta, to Mexico's Maya crude has narrowed this year by more than half to $11 a barrel. Heavy Canadian crude will cost the same in Houston as Maya arriving by tanker, including the cost of transportation, according to data compiled by Bloomberg.

Pemex widened the discount it gives U.S. buyers of Maya to $3.70 a barrel in January, from 90 cents in November. Pemex spokesmen didn't respond to several e-mails requesting comment on the company's market strategy.

Latin American producers will price their crude to make sure it's still attractive, said John Auers, executive vice president at Dallas-based Turner Mason & Co. an energy consulting firm. "It won't all disappear anytime soon," he said. The Gulf Coast "is the natural home for it."

Canadian output has grown in the past decade as rising prices made it economical to use steam recovery and bitumen mining in the Alberta tundra. Shipments to the U.S. rose 63 percent in five years to a record 3.1 million barrels a day as of September, U.S. Energy Information Administration data show.

The flow to the U.S. increased without Keystone XL, an $8 billion conduit that TransCanada Corp. wants to build from Hardisty to an existing network in Steele City, Neb. The project is awaiting a decision by the Nebraska Supreme Court on a legal challenge and then a final determination by President Obama's administration.

Enbridge Inc. operates a system that can ship 2.5 million barrels of crude from Canada to the Midwest and last month finished a line extending to Cushing, Okla. Enbridge and Enterprise Products Partners built the 450,000-barrel-a-day Seaway Twin to double capacity to Houston from Cushing.

TransCanada's existing system can bring 540,000 barrels a day from Canada to the Midwest, and the company built a 700,000-barrel-a-day line from Cushing to Texas last year.

While Canadian shipments have grown, imports from elsewhere fell. U.S. refineries took in 4.3 million barrels of crude a day from the rest of the world in June, the least since 1992.