The size of the oil slick at a well operated by U.S.-based Chevron Corp. off the coast of Rio de Janeiro state is more than 80 percent smaller than it was four days ago, said Brazil's National Petroleum Agency Tuesday.
The agency said in a statement that the slick at the water's surface covered 0.78 square miles (two square kilometers), compared to the 4.63 square miles (12 square kilometers) registered on Nov. 18.
The agency also said the oil slick continues moving away from Brazil's coastline.
Despite the announcement, Rio de Janeiro state's Environment Secretary Carlos Minc told reporters that in two weeks to a month the oil could reach beaches west of the city of Rio that are popular with tourists.
He said two-thirds of the leaked oil has still not risen to the surface and will "appear on the beaches of Angra dos Reis and Arraial do Cabo." These beaches are extremely popular with tourists.
The agency has said more than 110,000 gallons (416,300 liters) of crude oil may have reached the ocean floor since the leak began Nov. 7. Chevron said in a statement Tuesday that its estimate is slightly lower than that, at 100,800 gallons.
The Brazilian regulator's statement said the spill "is under control" and that only a small amount of oil continues oozing out of cracks on the ocean floor near Chevron's well.
"Oil takes a considerable amount of time to rise to the surface," the agency added. "So when more oil reaches the surface it won't necessarily mean there is a new leak."
On Monday, Brazil's environmental agency said it will fine Chevron nearly $28 million.
The agency said it will fine the oil company the maximum $27.6 million (50 million reais) allowed under current Brazilian law.
Brazil's Environment Minister Izabella Teixeira said that as an investigation into the leak continues, Chevron could face "five or six" other fines of the same amount if more infractions are found.
Chevron Corp. officials have accepted responsibility for the spill but reject accusations they didn't notify local authorities quickly enough or properly manage the cleanup.
"Chevron strongly asserts that its personnel were trained and prepared to address a potential incident of this type and responded immediately from the moment of first notification," the firm said in its Tuesday statement. "The company again notes that its combined efforts greatly diminished the size of the sheen and stopped the source of the seep flow within only four days of first detection."
George Buck, chief operating officer for Chevron's Brazilian division, has said the spill occurred because Chevron underestimated the pressure in an underwater reservoir.
Chevron was drilling an appraisal well about 230 miles (370 kilometers) off the northeastern coast of Rio state when crude oil rushed upward and eventually escaped into the surrounding seabed.
The oil has leaked through at least seven narrow fissures, all within 160 feet (50 meters) of the wellhead on the ocean floor.
The leak is a test for Brazil as huge offshore oil finds have been announced recently, with estimates that they could hold at least 50 billion barrels of oil.
Brazil has had bigger oil spills. In 2000, crude spewed from a broken pipeline at the Reduc refinery in Rio's scenic Guanabara Bay, dumping at least 344,400 gallons (1.3 million liters) into the water. Just a few months later, more than 1 million gallons (3.8 million liters) of crude burst from a pipeline operated by state-controlled oil company Petrobras into a river in southern Brazil.
Brazil's worst oil disaster was in 1975, when an oil tanker from Iraq dumped more than 8 million gallons of crude into the bay and caused Rio's famous beaches to be closed for nearly three weeks.