The Nabucco project can't entirely break Europe's dependence on Russian exports - it may in fact require supplies from Russia to fill its 31 billion cubic meters of capacity - but seeks rather to diversify the region's energy sources.
The prime ministers of Turkey, Austria, Bulgaria, Romania and Hungary signed a deal to allow the pipeline to cross their countries, linking Europe to gas resources in Central Asia and the Middle East.
Iraq, Egypt and Syria all said Monday that they were ready to contribute gas, as did Turkmenistan on Friday. Azerbaijan - one of the most likely contributors - said it is giving priority to the project.
"Nabucco will provide energy security to Turkey, to South East Europe and to Central Europe. Nabucco is thus a truly European project," said European Commission President Jose Manuel Barroso. "Turkey and the EU have tackled together a common challenge: the security and diversification of their energy supplies."
Russia provides over a quarter of Europe's gas, and 80 percent of that moves over Ukrainian pipelines. By diversifying imports and redirecting some of the Russian shipments through Nabucco, Europe could prevent a repeat of the January crisis in which all deliveries through Ukraine were suddenly cut off because of a price dispute. Still, Nabucco's impact is likely to remain small, as the volume of gas it can carry will be no more than 5 percent of Europe's consumption.
The United States, which is backing the Nabucco project alongside the EU, said it does not object to Russia's participation but argues Iran should be excluded until it improves its ties with the West. Washington said the pipeline would "help invigorate Europe" and strengthen U.S. allies.
Richard Morningstar, U.S. special envoy for Eurasian energy issues, and U.S. Senator Dick Lugar said Russia could possibly join the project.
"Russia can participate as a partner," he said. "We're trying to engage with Russia in the energy area. We don't want to see a zero-sum game."
Lugar said "we must explore how to improve confidence with Russia on energy."
However, Morningstar said Iran should be left out of the project until it improves its ties with Europe and the U.S.
"We don't believe Iran should be a participant," he said. "We have reached out to Iran. So far we have not had any positive response."
Morningstar said if Iran cooperates over its controversial nuclear program, "then one of the benefits would be for Iran to benefit from the energy sector."
The pipeline would not only make Turkey an alternative energy route between Central Asia and the Middle East to Europe but could potentially enhance Turkey's hand in overcoming EU resistance to letting it join the union.
"I believe that with the arrival of the first gas - and some experts have said this will be as early as 2014 - this agreement will open to door to a new era between the EU and Turkey," Barroso said. "Gas pipes may be made of steel, but Nabucco can cement the links between our people."
Turkey's Prime Minister Recep Tayyip Erdogan said Qatar could export liquefied natural gas to a projected facility in Turkey which can convert it and pump the gas to Europe through the Nabucco pipeline.
The 2,050-mile (3,300 kilometer) projected pipeline would run from the Caspian Sea across Turkey to Austria and involves investments of 8 billion ($10.26 billion), according to EU data.
Moscow, meanwhile, is pushing hard for new pipelines to Europe for its own gas - the so-called Nord Stream through the Baltic Sea to Germany and South Stream through Bulgaria.