The US and Mexico have reached common ground on key trade terms as pressure mounts to complete renegotiation of the 25-year-old North American Free Trade Agreement.
US President Donald Trump, a frequent critic of the existing deal, announced the apparent breakthrough on Monday.
The final outcome remains in doubt with Canada, the third country in the pact, due to rejoin talks on Tuesday.
Mr Trump has triggered a year of talks, after threatening to pull out of Nafta.
He demanded renegotiation of the 1994 trade agreement, which he blames for a decline in US manufacturing jobs, especially in the auto industry.
US shares rose and the Mexican peso strengthened on news of the preliminary treaty on Monday.
What has Trump said?
In a televised appearance at the White House, Mr Trump said the US and Mexico had agreed on terms that would make for an "incredible" deal that was "much more fair".
Negotiators have been rewriting the Nafta treaty over the past year, but in the last five weeks, Canada has not been part of the discussions.
"We will see whether or not we decide to put up Canada or just do a separate deal with Canada," Mr Trump said.
He also threatened Canada with tariffs on cars and said he wanted to get rid of the name Nafta, which he said has "bad connotations".
Where does Canada stand?
Canadian Prime Minister Justin Trudeau has spoken with Mr Trump since the breakthrough with Mexico was announced.
They "had a constructive conversation" and "look forward to having their teams engage this week with a view to a successful conclusion of negotiations," Mr Trudeau's office said. Canadian negotiators are set to meet their US counterparts on Tuesday.
Mr Trudeau also spoke to outgoing Mexican President Enrique Pena Nieto on Sunday, and the leaders shared their commitment to reaching a successful conclusion of Nafta "for all three parties".