UPDATE 1-TransCanada advances plan for pipeline to Texas

(Adds comment and detail. In U.S. dollars)

CALGARY, Alberta, April 25 (Reuters) - TransCanada Corp (TRP.TO) is already planning a major new oil pipeline to Texas from Alberta even as it breaks ground on building the $5.2 billion Keystone line to Illinois and Oklahoma, Chief Executive Hal Kvisle said on Friday.

TransCanada will hold an open season in the next couple of months to gauge oil shipper support for a pipeline with a capacity of about 750,000 barrels a day, Kvisle told reporters after his company's annual meeting. The line could be in service by 2012, three years after the first Keystone line is expected to be wrapped up.

"The construction (of Keystone) would roll into construction of the other," Kvisle said. "It's advantageous to us in terms of procuring pipe, the pipe mills can be kept busy longer, and in terms of securing contractors."

The line would run from the Empress pipeline hub in southeastern Alberta to Port Arthur, Texas, giving Canadian oil producers access to new customers among the refineries on the Gulf of Mexico, North America's biggest refining center.

The company has not released a cost estimate for the new line, however Kvisle said the pricetag may be much higher than it will pay to get the Keystone line into service, since Keystone uses old natural-gas pipes for part of its route.

"It will be a shorter overall distance because its a more direct route, but a greater overall cost because we can't use existing pipe," Kvisle said. "But the costs are not something we've finalized."

The project is one of a handful of proposals in the works to ship oil from Canada's burgeoning oil sands region to U.S. refiners. Production from the region is expected to nearly triple to 3 million barrels a day by 2015.

The firms operating in the region are seeking to extend their reach to avoid swamping refiners in the U.S. Midwest with oil and driving down prices. (Reporting by Scott Haggett; editing by Rob Wilson)