Chevron mandates coronavirus vaccines for some of its workers.

The oil and gas giant Chevron will require some of its employees to receive coronavirus vaccinations, becoming the first major U.S. oil producer to announce that it was requiring field workers to be protected against the virus at a time when other large corporations are making similar demands on office workers.

The mandate applies to employees who travel internationally and expatriates, as well as the offshore work force in the Gulf of Mexico and some onshore support personnel, the company said on Monday. Chevron is the second-largest oil and gas producer in the United States after Exxon Mobil.

“As part of our fitness for duty safety standard, workers in certain jobs are required to be vaccinated against Covid-19,” a Chevron spokeswoman said in an email. “We will continue to carefully monitor the medical data and follow the guidance of health authorities in order to protect our work force.”

The news was reported earlier by The Wall Street Journal.

Exxon Mobil does not have a formal mandate on vaccines, but the company is strongly encouraging workers to get vaccinated. A company spokesman, Casey Norton, said in a statement that Exxon was monitoring public health guidance.

“Given the spread of the Delta variant and its impact on unvaccinated individuals, all unvaccinated individuals are expected to wear a face covering in all indoor locations when six feet of social distance cannot be maintained,” he said. That policy went into effect on Aug. 18.

Like Exxon, Royal Dutch Shell encourages vaccination among employees, but it is not mandatory. Employees must comply with local laws requiring vaccination for entering public places or to enter countries. In some workplaces, Shell said, it may help ease vaccinations as a convenience.

Stanley Reed contributed reporting.