Work is due to start on Nabucco in 2011, with the first deliveries in 2014
Four European Union countries and Turkey have agreed to construct the long-awaited Nabucco natural gas pipeline.
Turkey, Romania, Bulgaria, Hungary and Austria have been working on the project - which will provide an important alternative energy supply to Russia - with the European Commission for seven years.
Here, readers from the five countries who agreed the deal, and other countries potentially affected by it, give their reaction.
This pipeline will break Russia's monopoly on natural gas. There will be five gas-supplying countries, unlike one - Russia - currently. Hopefully this project will also help reduce the ridiculous heating bills in winter.
Bora, Istanbul, Turkey
In theory it is a great project. But which countries are going to be the suppliers? What about Iran? If Nabucco will not be able to work efficiently because of the suppliers, Russia is going to be more powerful than ever. Good luck Europe
Deniz, Istanbul, Turkey
Of course having more choice will reduce the risk of energy shortages for both gas exporter and gas buyers in Europe and Turkey. This also means the monopoly of Russia will be weakened so Russia has to act as a fair trader in supplying gas. So we will likely face less crises like the one faced in Ukraine. Turkey is a reliable partner for gas exports because of its strong and independent economic institutions.
Hsagman, Istanbul, Turkey
The agreement still leaves many unanswered questions for the future of the project. Although the main target of the pipeline project is to bypass Russian natural gas through Europe it isn't accurate yet how the Nabucco consortium will find sufficient gas supply from natural gas-rich countries. In fact, I think Russia will try to prevent those countries which have immense amounts of gas sources by using its diplomatic power throughout the region.
We shouldn't forget that Russia is still the world leader with its large number of natural gas resources. So the only way for the European Union is to accelerate its renewable energy projects before 2020 to decrease its dependency on Putin's Russia. Even though Turkey's role is prominent in the region it will be a waste of time for it to approve the Nabucco project to the detriment of its diplomatic relations with Russia.
Erdem Sezer, Istanbul, Turkey
The Nabucco project is supposed to get gas from the Azeri and they appear to be selling the gas to Russian companies and that all sounds like a very classic scheme. In fact it is still the Russians who will benefit and control the supply. I doubt that the EU Commission will allow this, if they can do anything about it, that is. So I would assume we still don't know all the facts. What is very important in this matter is that there is as much alternative in supply lines and supply companies as possible, so there is competition and customers get fair prices. The rest is really a side issue, concerning those involved in the negotiations.
Adrian, Bucharest, Romania
Nabucco is a necessary project that will lessen the dependence on Russian gas. Both the South and Nord-stream pipelines remind us Eastern Europeans of the Ribbentrop-Molotov pact and therefore they are scary. They do nothing to reduce European dependence on Russia, but rather, they divide Europe, and circumvent the eastern states that lose any influence over the politics of energy. They are primarily aimed against Ukraine and Poland but other Eastern European countries might feel their adverse effects as well.
Drew, Cluj, Romania
Nabucco raises more questions than it solves, being in direct competition with the Russian South Stream project. Bulgaria, the only country to host both pipelines on its territory, will again have to manoeuvre between the interests of the EU and those of Russia, forgetting about its own.
Georgi Kantchev, Sofia, Bulgaria
For Bulgaria this project will bring diversification of the gas supply which is now 100% from Russia. But it poses many other important questions. Bearing in mind the massive political pressure is it possible that some other important aspects are being underestimated, such as environmental issues, and human rights concerns.
We know that Turkmenistan is a country with an almost dictatorial regime and that human rights there are brutally violated. How will the EU guarantee that money from the EU will not go towards the violation of human rights there. Maybe one option is for the EU to ask Turkmenistan to sign an agreement for transparency and accountability on those issues.
Daniel Popov, Sofia, Bulgaria
I am totally bullish about the Nabucco pipeline deal. During the last gas crisis, Hungary got through it only because the government had built up enough gas reserves in the summer. The reports from Bulgaria broadcast on your network at the time were harrowing. Whatever Mr Putin says, I would rather see Hungary among those who are building a better future, as far as gas supplies are concerned.
Peter Haley Dunne, Budapest, Hungary
Yes it will reduce Hungary's dependence on Russian gas. Unfortunately what it will not do is give Hungary any more control over its own economy and future, nor deal in any way with climate change or the democratic distribution of wealth. It's another step in a sad and boringly predictable path which lets the few dominate the many. Yawn. What about solar energy for Hungary? A real investment, not a quick buck, ensuring production, jobs, exports, land use, cash flow, environmental education, clean air, partnership and much more freedom from political games and corruption.
Timmy Green, Budapest, Hungary
I don't think that it will reduce the dependence on Russia. The present needs of Europe mean that this would only cover a small percentage of required supplies. I think that this is more a prestige project of the West and another step towards trying to secure Turkey's EU membership. Besides, the potential resource states, Azerbaijan, Iraq or Turkmenistan, are all far from being politically, economically or socially stable countries, which could be destabilised from one day to another very easily.
Arsen Gulistanyan, Vienna, Austria
The general dependence on Russia should hopefully reduce, but as for how effective the pipeline will be, this is still speculation and we can't say with absolute certainty. The Nabucco line though is still an ambitious project in my view, but not impossible. Let's just wait and see what time has to deliver.
Ashwin Karthik, Vienna, Austria
We should not be fully dependent on just one country or single source of energy, and this is a step towards remedying that. Considering Russia's strong opposition to the project, this project is special.
Giorgi Meladze, Tbilisi, Georgia
For sure, it is an historic project, having utmost importance for those depending on Russian gas supply. Nabucco is a serious blow for Russia. European countries will be more determined to demand Russia meets its obligations
Archil Maisuradze, Tbilisi, Georgia
Turkey is doing a lot for European interests, so I don't think it is right to keep Turkey outside of the European Union. How many European countries have done what Turkey has done for the rest of the European Union? I think Turkey should say enough is enough, and get out of any future partnerships with Europe. Europe doesn't deserve Turkey.
Logan, Moscow, Russia
For Britain and other Western states, Russia seems to be guilty of everything these days. The important thing about these three pipelines is that none of them goes through Ukraine, the real culprit, in my view, of the gas crisis of last winter.
T Payne, Serbia
It is an attempt by Turkey to strengthen its bid for EU membership. With the collaboration of Azerbaijan, Turkey will threaten the EU by cutting off the gas pipeline.
I wouldn't expect much to come of this project, because the source is Baku. The reserves there are variously reported to run out by the middle of the next decade, if not earlier. Besides which, the influence of the Kremlin is still rather strong in Azerbaijan, as Medvedev's visit and deal last week indicated. Expect to hear more from the South Stream project, or a Russia-trans-Black Sea-to-Turkey version of Nabucco, sidelining Ukraine and Georgia.
Nareg Seferian, Yerevan, Armenia
I think the Nabucco project is important for Europe and for Azerbaijan. It will strengthen Europe's relations with Azerbaijan and will make Europe less dependent on Russia.
Togrul, Baku, Azerbaijan
As an Azeri-Turk I would like to say it is a victory for Europe to reduce their independence on Russian gas, which has been used by Russia as a political hammer against European countries.
I work in the oil and gas industry and have worked on several projects relating to the Caspian region. This is an important development in the commercial development of Caspian Sea gas and will help demand from the gas pipeline recently built from the Caspian sea to the Turkish border with Georgia.
Ian Jackson-Reeves, London, UK