Iran seen as alternative to Turkmenistan in Nabucco gas project - Tehran Times
Turkmenistan agrees to supply EU with gas - French foreign minister - Forbes
EU and Turkmenistan Discuss Gas Export Possibilites - Oil and Gas Eurasia
Turkmenistan: Confusion Reigns About Ashgabat's Commitment To Nabucco - Radio Free Europe, Radio Liberty
Radio Free Liberty contrasts with the Forbes statements, suggesting in their article that Turkmenistan has made no concrete commitment to the Nabucco Pipeline. Both articles say Turkmenistan wants to diversify their energy exports, but Forbes implicates that this means the Nabucco Pipeline. However, Radio Free Liberty asserts that:
"I'm just coming back from a very interesting meeting with the president of Turkmenistan," Ferrero-Waldne said, "... All depends then on the market prices, and it will certainly also help to develop their market. But on the other hand, it will give [Europe] another supply source."
I like the Oil and Gas Eurasia quote:
""The partners reaffirmed mutual adherence to the search for new approaches to cooperation to ensure energy security," the Turkmen government said."
Whatever that means.
Most of those articles cite that Turkmenistan could change its mind.
Additionally, "..Turkmenistan already supplies some gas to Russian pipelines leading to Europe. So it still is not entirely clear by what route Turkmen gas will arrive in Europe." - RFLRE
Meanwhile, Oil and Gas Eurasia cites that the pipeline could end up going through Iran because of a deal between Turkey and Iran. They only cite Azerbaijan and Turkmenistan as suppliers however...
The Tehran Times goes to the next step and is the only source I found saying the following:
"Azerbaijan, Iran, Turkmenistan and, more recently, Iraq have been seen as possible suppliers for the project. Iraq is being backed by the United States."
EIA: Natural Gas Reserves by Billion Cubic Feet from World Oil and Oil and Gas Journal
4. Saudi Arabia
5. United States
???Azerbaijan and Iraq???