Judge Ralph Beistline also lifted BP Exploration (Alaska) Inc.'s probation altogether in a written order issued Tuesday.
BP was convicted of negligent discharge of oil in 2007 for a 200,000-gallon (757,000-litre) spill on the North Slope a year earlier.
There was another spill of 13,500 gallons (51,100litres) in 2009.
Last month, government lawyers sought to have BP's probation revoked for the latest spill, meaning the probation period could have been lengthened or the company could have faced additional penalties.
In his ruling, Beistline said the government failed to prove the company committed criminal negligence.