Brazil's state-run oil company Petrobras refined an average 2.03 million barrels a day of crude in the first 11 months of 2013, an amount equivalent to about 97% of its capacity.

That was an 8% increase over the same period of 2012 when Petrobras refineries averaged 1.9 million barrels a day.

Petrobras has been running its refineries at near capacity in an effort to reduce imports of gasoline and diesel fuel that are sold at a loss due to the government's fuel-price controls.

The company's 13 refineries are not able to keep up with rising domestic demand for gasoline and other products, forcing the world's sixth-largest economy to buy fuel supplies from as far away as the United States and India.

Union officials and oil industry experts say that pushing refineries so close to capacity is unsustainable over the medium and long term, raising the risk of accidents because of delays in maintenance.

Workers at a Petrobras refinery warned the company in October that a key unit now shut after a fire was "dangerously" above capacity, union officials told Reuters on Monday.

The blaze shut down the coking unit at the 242,000 barrel-a-day REDUC refinery in suburban Rio de Janeiro on Saturday. Petrobras said it expects to restart the unit on Friday and that the rest of the refinery was operating normally.

Industry experts say the unit is responsible for 30% of the refinery's gasoline and diesel output.

The incident at REDUC follows a November fire that put Petrobras' 200,000-barrel-a-day REPAR refinery near Curitiba, Brazil out of service for nearly a month and forced the company to hire a fleet of tankers to import emergency fuel supplies from as far away as India.

Petrobras rebuffed union criticism, saying in a statement that it maintains the highest maintenance standards. It said increased refinery processing was due to new units that came on stream in 2012, along with improved efficiency and the elimination of bottlenecks.

Petrobras announced earlier on Tuesday that it has completed plans to introduce diesel and gasoline with sharply reduced sulfur content in service stations throughout the country.

As of Jan. 1 all regular gasoline deliveries from Petrobras refineries have no more than 50 parts per million of sulfur, a corrosive pollutant that can seriously harm human health, the environment and property.

Petrobras also said that it has made diesel with 10 parts per million of sulfur available.

Diesel is Brazil's most-used vehicle fuel, but the S-10 diesel needed to make engines built to new emission standards function properly only accounts for about a quarter of Brazilian diesel demand. The rest of Petrobras output is S-500, fuel with 50 times more sulfur than S-10.

Petrobras said the new standards will not change Brazil's fuel import needs or the makeup and quality of fuels it imports.