As Republicans push the Obama administration for a quick decision on the Keystone XL pipeline, lawmakers sparred today over one of the proponents' central arguments: The pipeline will boost American energy security.

Supporters say the $7 billion pipeline, which would bring 800,000 barrels of crude daily from Canada's oil sands deposits to Gulf Coast refineries, would reduce U.S. dependence on oil from sometimes hostile foreign suppliers.

"If we go forward with the Keystone pipeline, for the first time in 60 years our country would have the opportunity to be independent of the current circumstances where we depend on the OPEC cartel," Rep. Ed Royce (R-Calif.), chairman of the House Foreign Affairs Subcommittee on Terrorism, Nonproliferation and Trade, said at a hearing.

But while upping imports from Canada may reduce the amount of oil the United States is purchasing from other regions, it won't insulate the United States from price shocks since the commodity is traded on a global market, several witnesses said.

"Even if we sharply reduce our oil import dependence, our economy and national security will remain tightly linked to the global oil market, especially the trends and events in the Persian Gulf," said Robert McNally, president of the Rapidan Group and former energy director at the National Security Council during the George W. Bush administration. "Oil is a fungible commodity that is widely traded on a global market ... a disruption or price shock anywhere means a price shock everywhere."

New supplies coming online in the Western Hemisphere, including Canadian oil sands crude and shale oil and gas in the United States, can help reduce U.S. vulnerability to those disruptions, but won't make it null, he said.

Republicans on the panel also emphasized American competitiveness -- arguing that the United States is competing with Asia not only for the oil, but for the manufacturing jobs that it supports.

Democrats, meanwhile, pressed the question of whether crude imported from the pipeline would remain in the United States.

"The Keystone pipeline would provide an export outlet, actually reducing supply in the U.S. by allowing oil companies to sell in higher priced markets elsewhere in the world," argued Rep. Gerry Connolly (D-Va.), who unsuccessfully proposed an amendment to the Keystone bill this summer to require that oil from the pipeline be used only within the United States.

Connolly and other pipeline foes argue that exporting the oil would undercut national security benefits.