Rafael Ramirez, the oil minister, said that the state oil fields would be seized if the deadline was missed.
Chavez was given the power to rule by decree on Wednesday and has vowed to nationalise key industries.
In Washington, the White House responded by saying it hoped US companies would be treated in accordance with international regulations.
Chavez reiterated that Venezuela would take a stake of at least 60 per cent in four projects which are developing crude from eastern Venezuela's Orinoco Belt into synthetic oil. He said he hoped the foreign companies would stay on as minority partners.
"I'm sure that they're going to accept this because we are going to continue being partners. Now, if they aren't in agreement, they are totally free to leave," he said.
The four Orinoco projects have a production capacity of around 600,000 barrels per day.
Chavez has promised to take over oil and gas projects in Venezuela, the fourth largest exporter of crude oil to the US, along with power utilities and the country's biggest telecommunications company.
Despite the Venezuelan president's will the takeovers could prove difficult.
A senior Venezuelan oil official has acknowledged that the country could face hundreds of millions of dollars in penalties if it takes over the projects because of financing agreements with international banks.
Ratings agency Fitch said Venezuela would be in default on some $4bn in project financing if the government unilaterally takes over the Orinoco projects.