The U.S. and New Zealand had proposed creating a reserve in the pristine Ross Sea. At 1.34 million square kilometers (517,000 square miles), the sanctuary would have been twice the size of Texas.
The proposal, a decade in the making, had been scaled back from earlier plans. Many countries hoped that would be enough to entice previous objectors Russia and Ukraine to agree. Those countries are among several that have fishing interests in the region.
But the 24 nations and the European Union failed to reach a required consensus as time ran out Friday on a 10-day gathering of national delegations in Hobart, Australia.
The countries also failed to agree on a second proposal to create smaller reserves in East Antarctica.
The Pew Charitable Trusts said Russia and Ukraine essentially ran down the clock filibuster-style after earlier expressing positive sentiments about the proposal.
"This is a bad day for Antarctica and for the world's oceans that desperately need protection," said Andrea Kavanagh, director of Pew's Southern Ocean sanctuaries project.
The Ross Sea is home to the Antarctic toothfish, a lucrative species that is often marketed in North America as Chilean sea bass.
The nations that make up the Commission for the Conservation of Antarctic Marine Living Resources are scheduled to meet again next October.
Kavanagh said she doesn't believe the sanctuary plan is dead, although she's not sure what it will take now to get it passed.