 Chavez will over the refineries as part of May Day celebrations |
Many of the world's biggest oil companies have agreed to transfer operational control to the government.
The May Day takeover comes one year after Bolivian President Evo Morales seized his country's gas fields.
Mr Chavez has also said he wants to pull Venezuela out of the International Monetary Fund and the World Bank.
The president said he had ordered Finance Minister Rodrigo Cabezas to begin formal proceedings to withdraw from the two international bodies.
President Chavez has spoken of his ambition to set up what he calls a Bank of the South, backed by Venezuelan oil revenues, which would finance projects in South America.
Compensation not guaranteed
The four projects to be taken over in the Orinoco Belt can refine about 600,000 barrels of crude oil a day.
Mr Chavez said he would take control of at least 60% of the projects, which were previously owned by ConocoPhillips, Chevron, Exxon Mobil, BP, Statoil and Total.
Negotiations are continuing about ongoing shareholdings and the possibility of compensation for the refineries.
Venezuela has only considered agreements based on the book value of the projects rather than their much larger current net worth.
Oil minister Rafael Ramirez has said that there may not be compensation at all in some cases.
More surprises
There will be more surprises from Bolivian President Evo Morales in his May Day address, one year after he shocked international investors by seizing control of the energy industry.
"It's going to be series of surprise measures, and if we were to announce them the day before it'd no longer be a surprise," Interior Minister Alfredo Rada said.
Local media reports have suggested that the measures could involve nationalising the mining industry.
The government had hoped to finish nationalising the telecoms industry by May Day, but talks with Telecom Italia - which owns half of the biggest telecoms company - are currently stalled.
Telecom Italia said last week that it was considering seeking international arbitration over the sale of Entel after Bolivia issued two decrees aimed at renationalising the company.
