The discovery of the largest gas field on land outside the USA and the Soviet Union in the Dutch province of Groningen in 1959 was the direct reason why a number of the world's oil companies began to show an interest in the North Sea.

Norway proclaimed its sovereignty over the Norwegian continental shelf (NCS) by a royal decree of 31 May 1963. This laid claim to the NCS "to such extent as the depth of the sea permits the exploitation of natural deposits, irrespective of any other territorial limits at sea, but not beyond the median line in relation to other states".

Passed by the Storting (parliament) on 21 June 1963, the Act relating to Exploration for and Exploitation of Submarine Natural Resources vested the right to these assets in the state.

The Petronord agreement, signed on 16 January 1964, covered collaboration between French oil companies and Norway's Norsk Hydro on exploring for and exploiting possible oil and gas resources on the NCS. The deal was initiated by the French companies and France's government.

The Continental Shelf Act of 1964 vested the right to the UK continental shelf (UKCS) in the British Crown.

The Continental Shelf Act of 1964 vested the right to the UK continental shelf (UKCS) in the British Crown.

A treaty was concluded on 10 March 1965 between Norway and the UK on how the continental shelf should be divided between them. It was determined that the median line principle would apply.

A royal decree of 9 April 1965 specified rules on exploring for and exploiting submarine natural resources.

Petropar Norge A/S (later Elf Norge A/S) was created on 15 June, just in time to submit an application in the first Norwegian offshore licensing round.

The Norwegian government announced on 13 April 1965 that 278 blocks were available for applications to secure exclusive production licences. The NCS below the 62nd parallel (which marked the northern boundary of the North Sea) was divided into 36 quadrants, each normally comprising 12 blocks which measured 15 minutes of latitude by 20 minutes of longitude.

"BP strikes gas...North Sea Klondike" blared the headlines in the British press after the Sea Gem self-elevating barge (jack-up rig) struck gas in the southern North Sea, 68 kilometres off the River Humber. Later named West Sole, this was the first hydrocarbon discovery on the UKCS and the outcome of Sea Gem's fourth well in these waters.

France's state oil companies RAP and BRP (Elf) merged in December 1965 to create Enterprise de Recherches at d'Activités Pétrolières - Erap. This marriage took effect on 1 January 1966.

The Petronord group initiated a number of seismic surveys on the NCS south of the 62nd parallel in 1965, and possible petroleum resources were identified the following year in what later became the Frigg area.

The Elf name and logo were introduced on 27 April 1967. In the early 1960s, several French companies involved in oil product sales - Caltex, La Mure, CFPP, Avia and Lacq - had been merged under Union Générale des Pétroles. This created the need for a common trademark to be used on service stations and the like.

Before the first licensing round, Petropar - later Elf - had no form of organisation or employees in Norway.

The first well for the Petronord group was spudded by Ocean Viking in block 16/6 on 7 November 1967. The well was the 10th on the NCS and was drilled in 117 metres of water to a total measured depth of 2 016 metres and completed in mid-January. It was found to be a duster (dry).

The Ministry of Industry put 68 new blocks on offer in the North Sea on 21 May 1968.

The first hydrocarbon discovery on the NCS occurred on 15 June 1968 in the field later known as Cod, operated by Phillips Petroleum Company. Consisting primarily of gas and condensate (light oil) with a little oil, this discovery boosted optimism.

Ekofisk has been nicknamed "Norway's big Christmas present". The final exploration well in block 2/4 was plugged on 23 December 1969 in the knowledge that a major discovery had been made.

The Frigg Field lies in blocks 25/1 and 10/1.

The Petronord group gave its big gas discovery in block 25/1 the name Frigg, after the most prominent goddess in Norse mythology. This field was the first of a number on the NCS to be given names taken from the old Norse myths.

The Ekofisk discovery marked a dividing line in Norwegian oil history. Once they knew that oil and gas were present on the NCS, Norwegian politicians and industrial interests became more self-conscious. They began to call for participation and to secure a share of profits from the oil business.

The Petronord group spudded its first wildcat (exploration well) in the area identified as promising by seismic surveys during the spring of 1971. Pilot production was due to begin on Ekofisk that summer, and optimism about North Sea exploration was much greater than before. A number of discoveries had also been made in the British sector.

Elf Norge AS had offices in both Oslo and Stavanger from 1967. Administrative functions were based in the capital, while the technical department head by Paul le Rest was in Stavanger. Immediately after the discovery of Frigg in 1971, it was resolved to move the administrative department to the latter city.

Ocean Traveler spudded a well in UK block 10/1 during January 1971, but the work had to be suspended because of storms.

Several development concepts were submitted to the coordination office for the Frigg project for consideration.

The Ministry of Industry declared officially that the operators regarded Frigg as commercially exploitable. It was regarded at the time as the largest offshore gas field to have been discovered worldwide.

Since Elf moved to Stavanger in 1967, it had leased a base area and office building from Torolf Smedvig and Norsea at Strømsteinen. The discovery of Frigg and the transfer of administrative functions from Oslo soon made these premises too small.

The Frigg reservoir straddles the boundary between the Norwegian and British North Sea sectors. While the TOM group was the UK licensee, with Total as operator, Elf-operated Petronord held the rights on the Norwegian side.

The Norwegian government exercised its option to take a five per cent holding in the Petronord group on 25 May 1973.

The Frigg licensees concluded an agreement in principle on unitising the gas resources on 9 July 1973. This Frigg main agreement specified that the field should be treated as a unit and that the final return to each licensee would depend on their share and the division of the reservoir between Britain and Norway.

The third licensing round on the NCS was announced on 11 July 1973, having been postponed time and again since notice of it was first given in 1971.

East Frigg was a satellite of Frigg which lay in 110 metres of water 18 kilometres from the main field. The production licences were numbered 024 and 026 for blocks 25/1 and 25/2 respectively, awarded in the second licensing round in 1969, and 112 for block 25/2 awarded in 1985.

Many Norwegians remember the winter of 1973 for the car-free Sundays, part of the curbs on consumption imposed because of the oil crisis.

Esso discovered the Odin gas field in Norwegian block 30/10 on 28 March 1974. The reservoir lay between 1 997 and 2 067 metres below the drill floor of the Drillmaster rig.

Odin was the principal Norse god and dwelt in Valhall. Married to Frigg, he was also known as the All-Wise.

Elf discovered North-East Frigg in the spring of 1974, when Deepsea Driller encountered a 60-metre gas-bearing formation at a depth of 1 920 metres beneath the seabed. The field was located 18 kilometres north-east of Frigg in block 25/1.

According to the "10 oil commandments", Norwegian petroleum should be landed as a general rule in Norway.

Construction of what was intended to be the first installation on Frigg, the DP1 drilling platform, began in the summer of 1973. The steel jacket was due to be positioned on the field the following summer.

Frigg was the world's largest offshore gas field when development began.

Jean Curutchet was put in charge of Frigg in 1976, and eventually earned the nickname "Mr Frigg". He was supported by a technical vice president, responsible for coordinating and controlling the industrial sub-projects, and a chief controller.

The Alwyn area was licensed in 1965 to Total Oil Marine (33.33 per cent) as operator and Elf UK (66.67 per cent). This acreage lies on the UKCS 160 kilometres east of Shetland, 440 kilometres north-west of Aberdeen and 110 kilometres north of Frigg.

The quarters platform (QP) provided accommodation for the three central installations on the field. It was also the nerve centre for Frigg, with control room, helideck and telecommunications.

Concrete drilling platform 1 (CDP1) was a drilling and production installation on the UK side of Frigg.

The flare platform was designed jointly by Elf and the Compagnie Française d'Enterprises Metalliques (CFEM) yard.

The level of press interest increased after the loss of the DP1 jacket on 12 October 1974.

During drilling to determine the extent of the Frigg field and its division between Norway and the UK, Petronord discovered the Lille-Frigg satellite in block 25/2 during 1975.

During platform installation on the field, the need arose to accommodate the workforce during this hectic construction period. The quarters platform would not be ready for occupation before 1977, which meant that a temporary solution had to be found.

With effect from 1 January 1976, a separate project team was created for each of the platforms.

Société Nationale Elf Aquitaine (SNEA), usually known as Elf Aquitaine, was created on 1 January 1976 by merging French state oil companies Elf (ERAP) and Aquitaine (SNPA).

The final treaty between Britain and Norway over Frigg unitisation was signed by representatives for the two countries in London on 10 May 1976.

Drilling and production platform 2 (DP2) stood on the Norwegian side of Frigg.

The 14/9 manifold compression platform (MCP-01) was installed in June 1976, about midway between Frigg and St Fergus in Scotland.

Treatment platform 1 (TP1) was one of two gas treatment installations on Frigg. It stood on the UK side of the boundary and processed gas from concrete drilling platform 1 (CDP1) prior to transport through the British pipeline to St Fergus in Scotland.

Ever since Fredric Isoard had been posted to Norway as managing director of Elf Norge AS in 1976, he had worked to achieve good communication with the employees. He took the initiative three months after his arrival on establishing a joint staff-management committee.

After swift consideration, the Norwegian Storting (parliament) unanimously approved "the agreement between the government of the United Kingdom of Great Britain and Northern Ireland and the government of the Kingdom of Norway relating to the exploitation of the Frigg field reservoir and the transmission of gas therefrom to the United Kingdom", to give the Frigg treaty its full official name.

The Elf Aquitaine Norge Offshore Union (Eanof) was founded in May 1977 to function as a house union for Frigg employees. It was modelled on the Ekofisk Committee, which had existed since 1973.

The Petronord agreement was concluded on 1 September 1965 for a period of 12 years. When it expired on 20 June 1977, Hydro opted to withdraw from this collaboration.

Treatment compression platform 2 (TCP2) processed gas from the DP2 drilling platform, and eventually also from the North-East Frigg, Odin, East Frigg, Lille-Frigg and Frøy satellites.

The quarters platform (QP) was ready for occupation in the summer of 1977. Each of the four stories above the bottom deck covered 1 000 square metres.

The Directorate of Fisheries received constant complaints in the mid-1970s from Norwegian fishermen whose gear had allegedly been damaged by scrap on the seabed. No less than 1 200 such reports were received from all over the North Sea in 1976 alone.

Nurse Svanhild Rolfsen received permanent appointments on Frigg in August 1977 as probably the world's first woman employees offshore.

The Storting (parliament) resolved in 1974 that every Norwegian company with more than 50 employees should have a working environment committee (AMU) to deal with all work conditions.

Once oil and gas had been extracted from fields in the Northern North Sea, they had to be brought ashore to be processed and distributed. The coastal village of St Fergus in Aberdeenshire was not the first choice for the Frigg gas processing plant. Initially, planning permission was sought to build the terminal several miles away on the disused airfield at Crimond, next to the Loch of Strathbeg, Britain?s largest coastal dune lake.

Treatment platform 1 (TP1) processed and dewatered gas transferred from drilling platform 1 (DP1) before it was transported through the Frigg UK Pipeline to Scotland.

The field was opened for production on 13 September 1977, after the first seven wells drilled from CDP1 had been completed.

Drilling of production wells from CDP1 began on 10 November 1976.

Norway's Companies Act required the creation of a corporate assembly in all companies with more than 200 employees. Such a body was established by Elf on 1 October 1977.

The first production well to be drilled from drilling platform 2 (DP2) was spudded in November 1977, and first gas was produced from this installation in August 1978 - one year after CDP1 came on stream.

Although agreement on developing Frigg had been reached between the licensee groups and between Norway and Britain, and the unitisation agreement was put in place in 1976, the size and division of the field remained to be clarified.

HM King Olav V of Norway undertook the official inauguration of the Frigg field on 8 May 1978. Arriving by helicopter, he was greeted by representatives of the UK government and the Frigg group, headed by Elf Aquitaine.

St Fergus and the pipelines were successfully tested on the 11th September 1977 and became fully operational on the 13th. On 9th May 1978, Queen Elizabeth II and the Duke of Edinburgh arrived at St Fergus to officially inaugurate the terminal. A day previously, the King of Norway had presided over the official Frigg Field ceremony.

Fifteen blocks were put on offer in Norway's fourth offshore licensing round. The government wanted to avoid a decline in the level of activity on the NCS and to secure a better overview of total reserves below the 62nd parallel.

Frigg was developed in several stages. Phase I was completed when the British side of the field came on stream in September 1977. The second phase involved installation of the Norwegian facilities - drilling platform 2 (DP2) and treatment compression platform 2 (TCP2).

A new oil crisis broke out in 1979 following the revolution in Iran.

A new tax treaty was agreed between the UK and Norway in 1979, which included provisions concerning Norwegian personnel working on the UKCS. This agreement had direct consequences for employees on Frigg, which had three platforms on the UK side and two in the Norwegian sector.

A powerful explosion was heard all over the Frigg complex at 15.30 on 7 September 1979, and the gas leak alarm sounded on TCP2. The hatch on the CM2 pig receiver in the flowline system from DP2 had failed.

A 10 000-tonne barge from Heerema began drifting towards Frigg on 13 December 1979.

The union for land-based employees was established in response to Eanof, the house union for offshore employees. Its object was to organise local employees in Elf Aquitaine Norge (EAN) on land to protect and promote their financial, professional, cultural and environmental interests and to work for solidarity and a good, trust-based relationship with the company.

Elf moved into new offices in Dusavik in 1975. However, the organisation steadily swelled as the development of Frigg advanced and the start of production approached, and larger premises were required.

The radio shack on Frigg received a message from the Rogaland Radio station on the mainland at 17.30 on 7 May 1981 that there was an injured man on a fishing boat. Arne Bråten, Odd Myrvang and Steinar Vestrheim, the crew of the Bell 212 helicopter, got ready for a mercy mission. This machine was normally used for shuttle transport between the Frigg platforms, but was also equipped for sea-air rescue.

In the spring of 1974, Elf Northeast Frigg was discovered when the "Deepsea Driller" drilling rig found a 60 meter thick gas pocket, 920 meters below the seabed.

The pressure in the Frigg reservoir declined as the gas was produced. Since the British Gas Corporation required deliveries at a constant pressure, equipment had to be installed on Frigg to achieve this in the pipeline.

Opening an office in the north Norwegian port of Harstad in June 1982 made Elf one of the first oil companies to set up shop in this part of the country with its own exploration department.

Forty blocks were put on offer in 1983 in the North Sea, the Halten Bank in the Norwegian Sea and the Tromsø Patch in the Barents Sea.

Modules were installed on TCP2 during 1983 to permit the reception and treatment of gas from the Odin and North-East Frigg fields.

Frigg's first woman employee joined the workforce in 1977. The next milestone for women offshore was passed when Anne Grete Ellingsen started her job as offshore installation manager (OIM) for DP2 on 18 January 1983. She was the first female in the world to hold such a position.

The Odin field was regarded as commercially marginal, and the emphasis was accordingly on low-cost technical solutions.

The worst diving accident in Norwegian history occurred at 04.00 on 5 November 1983 on the Byford Dolphin rig.

Production began on 8 December 1983 from the first three wells on North East Frigg. But it was not until a month later that petroleum and energy minister Kåre Kristiansen pressed the button in the control room on QP to inaugurate the satellite field.

Frigg was always a stable supplier of natural gas to the UK.

Anna Marie Sæ and Jorunn Oltedal became the first female operators on TP1.

The Odin field was regarded as commercially marginal, and the emphasis was accordingly on low-cost technical solutions.

A project team was appointed in 1985 to assess opportunities for reorganising production from Frigg.

The Heimdal platform was the largest steel structure on the NCS when it began production on 13 December 1985.

This field is named after the Norse god Heimdall.

The high oil prices of the early 1980s had encouraged new field developments on the NCS. Most oil-producing countries also exported as much as they could while prices were good. It turned out that Opec was unable to regulate the volume of oil produced.

Elf Aquitaine Norge made its first oil discovery in the autumn of 1987, about 32 kilometres south-east of Frigg.

Frøy - known in English as Frey - was the god of fertility in Norse mythology.

The Alwyn North field became the centre for the Alwyn area, supplying the other installations with electricity and water. It was developed with two platforms - North Alwyn A and B (NAA and NAB) - linked by a bridge.

The Norwegian authorities were keen to promote research into alternative offshore development solutions. In that context, Skuld was a government-sponsored research programme which involved a number of large companies and scientific institutes, including Elf, Statoil, Hydro, Kongsberg Våpenfabrikk (KV), the Norwegian Underwater Institute (NUI) and Sintef.

East Frigg was developed on the basis of the results from the Skuld project. It was the first field in the North Sea to be developed entirely without diver assistance in installing seabed templates, the manifold and the flowline system. Nor was diving used during production, with all maintenance carried out remotely from the surface.

French oil companies Coparex and Eurafrep merged with Elf in 1989, increasing the latter's holding in Ekofisk from 7.594 per cent in 1988 to 8.449 per cent in 1990.

New drilling technology made it possible by 1990 to reach the whole Frigg field from a single drilling platform.

Total Marine Norsk AS changed its name to Total Norge AS (TN) on 2 January 1991 in order to provide a clear and better defined external identity.

The alarm sounded in the main control room on Frigg at 09.39 on 10 November 1992: "A fire has broken out in one of the TCP2 shafts". Personnel were immediately ordered to evacuate the platform, and 70 people crossed the bridges to QP via TP1.

After just under 10 years of operation, North-East Frigg ceased production on 8 May 1993.

Three production wells were drilled on the Lille-Frigg satellite by Mærsk Jutlander from February 1992 to November 1993.

The Odin field was shut down on 1 August 1994 after producing 27.3 billion standard cubic metres of gas and almost 1.3 million barrels (200 000 scm) of condensate over more than a decade. Its gas had been sold to the British Gas Corporation.

The Frøy field was developed with an unstaffed wellhead platform - an installation which allowed the wellheads to be moved from the seabed to the surface.

After just under 10 years of operation, North-East Frigg ceased production on 8 May 1993.

Aker Maritime was the main contractor for removing the Odin platform.

It became clear in the early 1990s that the profitability of Frigg production was declining. A shutdown of the whole field would be only a few years off unless operating costs could be reduced.

East Frigg was shut down on 22 December 1997 after producing 9.2 billion cubic metres of gas and 625 000 barrels (100 000 scm) of condensate (light oil) over nine years. The five production wells were plugged during the first half of 1999.

The Heimdal operatorship in the North Sea was transferred to Norsk Hydro on 1 January 1998.

The British gas market was liberalised in 1996-98, and organised as a spot market - one in which the contracts traded are relatively short-term and come into force immediately.

A contract was concluded with Aker in 1999 covering maintenance on Frigg during the final phase.

The Lille-Frigg field was shut in on 25 March 1999, after producing 2.2 billion standard cubic metres of gas and 8.2 million barrels (1.3 million scm) of condensate (light oil).

Oil price fluctuations serve as a ruthless barometer, with a big impact on the level of activity in the petroleum industry. After a brief peak during the Gulf War in 1991, crude prices remained stable at USD 15-17 per cent for much of the rest of the decade.

The Norwegian pipeline from Frigg to St Fergus in Scotland became part of Norway's Vesterled transport system in 2001, together with a link to the Heimdal platform. This meant it was no longer called the Frigg Norwegian Pipeline (FNP). The Norwegian share of the receiving terminal in St Fergus was incorporated in the Vesterled system.

Production from two of Frøy's wells ceased as early as 1998. A cessation plan for the field was prepared by Elf in the autumn of 1999, and production ended permanently on 5 March 2001.

The cessation plan for Frigg was submitted to the British and Norwegian authorities in November 2001.

Total E&P Norway AS became the new official name in May 2003 for the merger between Total, Elf and Fina in Norway.

The process for approving the cessation plan for the actual Frigg installations got seriously under way in 1999, and it took the operator Total E&P Norge five years to secure final approval.

The Frigg field was shut down at exactly 07.00 on 26 October 2004. After 27 years of continuous and reliable operation, the norwegian sector had delivered 116 billion cubic metres. Exported entirely to the UK, this production was worth NOK 95 billion in 2007 money.