The European Union backs the project to help lessen its dependence on Russian gas, but Turkey's claims on the fuel were one of many potential obstacles for the 3,300-kilometer pipeline.
"The 15 percent out-take is not on the table," Nabucco managing director Reinhard Mitschek said.
"No deal breaker is on the table, and I am confident that Turkey as well as Europe will feel comfortable with the compromises reached."
A deal between Turkey and European governments on transit agreements for the pipeline should be signed on time in June, he said.
Russia opposes Nabucco and has accelerated plans for a rival project, South Stream, to keep its grip on Europe's gas market.
"Nabucco is not an anti-Russian project, but a pro-European project," Mitschek said. "We will need the Russian gas in the future for Europe. In addition to that, we will also take alternative gas on board."
A final investment decision should be taken on Nabucco in early 2010, he said, and construction was scheduled to start in 2011 to ship the first gas in 2014.
Iraq's Kurdistan heralded a plan to export gas from the semiautonomous region through the pipeline last month, although the central government rejected the scheme. Baghdad has also said it could supply Nabucco from another part of Iraq.
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