“The partners who signed are betting on a secure future in our fatherland,” Mr. Ramírez told reporters.

Still, these companies’ acceptance of the new rules in Venezuela and the potential exit of Conoco and Exxon point to concern that developments in Venezuela may influence negotiations over oil and natural gas projects in other countries, from rising African oil producers like Angola to longtime members of the Organization of the Petroleum Exporting Countries like Iran.

“What happens in Venezuela is something the Russians will look at, and may have bearing on places like Iran, Nigeria and other countries,” said Amy Myers Jaffe, an oil analyst at the James A. Baker III Institute for Public Policy of Rice University.

Oil is at the heart of a broader nationalization push that also includes large telecommunications and electricity companies. Mr. Chávez is trying to give his government a stronger hand in Venezuela’s economy even as the oil industry, by far the country’s largest source of revenue, struggles to maintain anemic production levels.

Michael J. Economides, an oil consultant in Houston, said Venezuela could benefit in the short term if fears over production translate into higher global oil prices. “If he produces 1 percent less,” Mr. Economides said in reference to Mr. Chávez, “the world market responds to that and he gets 20 percent more revenue over a period of time.”

Industry analysts put Venezuela’s output at about 2.3 million barrels a days, including more than 400,000 barrels a day from the heavy oil projects. Venezuela’s government says overall production is closer to 3.2 million barrels a day.

But with public spending surging under Mr. Chávez and with oil companies from Brazil, China and India hesitant to make major investments in Venezuela while legal uncertainty persists, energy analysts have cautioned that Venezuela’s government risks allowing prized reserves to remain underdeveloped.