Chevron was given the green light to resume oil exploration in Brazil following a massive 2011 spill which led to the US oil giant halting its activities, authorities said Monday.

The National Petroleum Agency (ANP) said it had approved Chevron's plan to resume production in four wells of the Frade oil field, located some 370 kilometers (230 miles) northwest of Rio, for a period of 12 months and in two other wells for a period of two months.

ANP said it would keep Chevron activities under constant surveillance.

The agency's ruling, made Friday but communicated to the press only Monday, stated that reports would be produced every two weeks on "monitoring and interpretation of pressure variations in the wells to assess the risks of variations in the geo-mechanical conditions of the reserves."

In November 2011, some 3,000 barrels of crude spilled into deep Atlantic waters in the Frade field, and Chevron admitted responsibility for the disaster.

As a precaution, Chevron voluntarily interrupted its Brazilian activities in March last year, after detecting another leak three kilometers (1.8 miles) from the first.

Last August, a Brazilian court ordered Chevron and its driller Transocean to stop their oil drilling and shipping activities within 30 days.

In September, ANP slapped a $17.5 million fine on Chevron for 24 violations linked to the spill.

The US oil giant operated only in the Frade field with a small output of 60,000 barrels a day.