The summit was also attended by Evo Morales and Daniel Ortega, the respective presidents of Bolivia and Nicaragua, and Carlos Lage, Cuba's vice-president.
Chavez did not specify how much oil he would be ready to sell at a 50 per cent discount.
Venezuela is already selling oil to Caribbean countries at a 40 per cent discount.
A leading member of the Organisation of Petroleum Exporting Countries (Opec), Venezuela plans to produce about three million barrels of crude oil a day in 2007
Half that planned amount is being sold to the US but Chavez is trying to forge anti-US alliances throughout Latin America and the world at large.
"We seek integration among our people rather than among our markets"
Carlos Lage, vice-president of Cuba
He remains critical of US plans to create the Free Trade Area of the Americas, a proposal to abolish or relax trade barriers between nations on the American continent.
Rene Preval, Haiti's president, and Maria Fernanda Espinosa, Ecuador's foreign minister, also attended the summit as observers.
Chavez said Haiti will also be eligible for the 50 per cent discount on oil.
In an opening speech to the summit, Ortega stressed efforts to "put an end to imperialist and capitalist domination" in the region.
Lage emphasised the importance of political integration over joint economic projects.
"We seek integration among our people rather than among our markets," he said.
Morales criticised the US free trade zone plan, calling instead for "fair trade that allows countries to solve their economic problems".
The Bolivarian Alternative was launched in 2004 by Cuba and Venezuela. Bolivia joined it last year, with Nicaragua following in January.