Oil spilled from the Tern platform 105 miles north-east of Lerwick this week but authorities say there was no environmental damage.
Twenty-three tonnes leaked on Tuesday from the platform operated by TAQA Bratani, owned by the Abu Dhabi National Energy Company which bought over most of the Brent system from Shell in 2008.
A Marine Scotland spokesman said: “There is no ongoing leakage or further issue as far as we understand.
“Due to the remote location of the rig, and the fact it was very rough weather at the time, we understand the oil dispersed quickly.
“We do not believe there are any environmental concerns at this time.”
However Stan Blackley, chief executive of Friends of the Earth Scotland, said: “This significant oil spill happened off the north-east of Shetland just two days before the UK Government gave consent to BP for oil exploration in the deep waters off the north west of Shetland.
“How strange that we should only hear about it after that announcement, even though it happened beforehand and the UK Department of Energy was aware of it! Once again, we see suggestions that the UK government is in cahoots with the big polluters.
“Only yesterday we were warning that Scotland should be seeking to end its addiction to oil and instead investing in clean, renewable energy solutions, and today we see yet more evidence of why this really must be the case.”
A spokesman from TAQA Bratani said the leak was the result of a “temporary upset in the production process whilst cleaning up a new well”.
Derek Howden, TAQA health, safety and environment manager, said: “We immediately put into action our response plan which outlines the steps to be taken in the case of any hydrocarbon release.
“In close cooperation with DECC it was agreed that the best action, with the least impact on the environment, was to let the oil disperse naturally rather than using a dispersant.
“This strategy was successful and the oil has since dispersed. TAQA immediately set up an investigation team to learn the lessons and prevent recurrence.”