Greenpeace stopped the dumping of the Brent Spar and other at-sea installations, in a campaign against using the oceans as a dumping ground.
Dramatic visual footage of activists being attacked with water cannons and relief teams being flown in by helicopter brought the stand-off to a massive audience.
Spontaneous protests in support of Greenpeace and against Shell broke out across Europe. Some Shell stations in Germany reported a 50 percent loss of sales. Chancellor Kohl raised the issue with the UK government at a G7 meeting.
But despite the UK government's refusal to back down on plans to allow the Spar to simply be dumped into the ocean, public pressure proved too much to bear for Shell, and in a dramatic win for Greenpeace and the ocean environment, the company reversed its decision and agreed to dismantle and recycle the Spar on land.
The decision led to a ban on the ocean disposal of such rigs by the international body which regulates ocean dumping.
Although the Brent Spar campaign is remembered as one of the most significant Greenpeace successes of the 1990s, it was actually just one part of a much larger campaign in which Greenpeace continues to confront industry and governments, challenging them to take action to protect the oceans.
Long before Greenpeace succeeded in stopping the disposal of obsolete oil installations at sea, we put an end to ocean dumping of radioactive and industrial waste.
These earlier campaigns, started in 1978 and 1980 respectively, culminated in 1993 in a worldwide ban on the dumping of radioactive and industrial wastes.
Before the Brent Spar campaign, a number of oil companies had been planning sea-dumping of obsolete installations, such as oil storage buoys (like Shell's Brent Spar) and oil rigs.
Greenpeace's action, and the support of people throughout Europe, ensured that no such structures have been dumped to this day.
For all the controversy surrounding the Brent Spar, this is the single most important outcome of the episode.
The Spar set a precedent for a more open and responsible approach from the offshore oil and gas industry to the decommissioning of obsolete platforms.
Towards the end of the campaign, in the absence of official figures, Greenpeace released its own estimate of the amount of oil left on the Brent Spar. However, we quickly realised that our improvised measurements had been taken from the wrong part of the Spar, resulting in a significant overestimation of the amount of oil left in the storage tanks.
As soon as it became aware of the error, Greenpeace proactively apologised. Although almost unreported at the time, the estimate subsequently became notorious and a persistent media myth was born - that Greenpeace had 'got it wrong' over the entire Brent Spar issue.
But the amount of oil left on the Brent Spar was never central to the campaign. The prime issue was, from the very beginning, the need for the offshore industry to take proper environmental responsibility for its obsolete platforms and other wastes, rather than using the oceans as a dumping ground.
In fact, many of the key points of Greenpeace's scientific rationale for opposing the dumping were supported and reinforced the following year by a committee set up by the Natural Environmental Research Council (NERC) at the UK Government's request.
Even the conservative Daily Telegraph noted that the NERC report 'vindicates many criticisms by Greenpeace last year of the Government's secretive policy of sea disposal for large oil installations'.
The Spar was eventually brought ashore in 1998 and recycled, being used as the base for a new quay in Norway. All the evidence has since shown that, as Shell itself later concluded, recycling the Brent Spar was the most environmentally sound option.
Without doubt, if the Spar had been dumped, many more platforms would have followed. There would have been little, if any, international scrutiny of decommissioning operations - and there would have been a cumulative environmental impact way beyond that of the Spar alone.
The Times summed it up in January 1997 when it identified the dumping of the Spar as 'all too clearly a precedent for dumping everything else from the North Sea into a giant underwater scrap heap.'
The following brief chronology highlights the major events of the conflict:
1st Executive summary of Greenpeace report on decommissioning, "No Grounds for Dumping" is sent to the UK Department of Trade and Industry. The report highlights recycling options for oil rigs and land-based disposal options.
16th Tim Eggar (DTI) announces the Government's decision to dump the Brent. Spar
29th Greenpeace vessel Moby Dick leaves Lerwick for Brent Field.
30th Greenpeace lands activists aboard the rig and occupy the Brent Spar.
10th UK Government grants Shell site licence to dump Brent Spar.
16th All opposition parties in the UK condemn the dumping of the Brent Spar.
17th In Belgium, ministers for foreign affairs, the environment and trade, condemn the British Government for allowing the dumping of the Brent Spar.
Iceland urges the British Government not to dump the Brent Spar.
23rd Shell removes Greenpeace activists from the Brent Spar.
2nd Greenpeace supporters start leafleting petrol stations and motorists at over 300 locations throughout Germany.
9th Environment Ministers at the North Sea Conference agree, with reservations from the UK and Norway, that it is unacceptable to dump offshore installations at sea and recommend the decommissioning of platforms on land.
12th Towing of Spar to deep sea dump site begins.
15th In Germany, some Shell petrol stations are reporting 50% loss in income as protests against dumping the Brent Spar increase.
16th Second occupation begins as two Greenpeace activists are landed on Spar by helicopter.
16th Chancellor Kohl raises Brent Spar issue with John Major at G7 summit.
16th The results of samples taken by Greenpeace during the first occupation are released, estimating a potential for up to 5000 tonnes of oil to be on the Brent Spar. Greenpeace subsequently found this to be wrong and admitted the mistake. The presence or absence of oil in the rig had not been the basis of Greenpeace's opposition to the dumping; nevertheless, Shell, several politicians and some media outlets suggest that Greenpeace's error in sampling data undermined the case against dumping the rig.
20th Shell reverses its decision to dump the Brent Spar. The 14,500 tonne oil installation is towed to Erfjord in Norway - it has been moored there ever since.
26-30th All members of the Oceans regulatory body OSPAR (with reservations from UK and Norway) agree on moratorium leading to a ban on the dumping of installations at sea. (Decision 95/1).
4th OSPAR moratorium (decision 95/1) comes into effect.
1st Michael Meacher (Environment Minister) announces that there will be 'no more Brent Spars under Labour'.
13th Independent foundation Det Norske Veritas (DNV), commissioned by Shell, produces its assessment report of the 8 disposal options open to the oil company. Dumping is listed as the worst environmental option.
3rd Shell announces that it has received official bids from 6 contractors outlining 9 disposal options.
29th Shell announces plans for disposal of Brent Spar in Norway.
30th Environment Ministers from Sweden, Denmark and Iceland as well as Klaus Kinkel, the German Minister for Foreign Affairs and Ritt Bjerregaard of the EU, welcomed the Brent Spar decision and the precedent they hoped it would set for other offshore installations.
23rd In Sintra in Portugal Environment Ministers at the Ministerial Meeting of the Oslo-Paris (OSPAR) Commission vote unanimously for a full ban on the dumping of steel offshore installations in the Northeast-Atlantic and the North Sea.
The British-Norwegian consortium Wood-GMC begins the decommissioning of the Brent Spar.