Nabucco is one of several European pipeline groups vying for the right to export Azerbaijan's gas in a competition which may reshape future gas flows to the continent. Its smaller rivals include the Interconnector Turkey-Greece-Italy (ITGI) and the Trans Adriatic Pipeline (TAP).

Saturday is the deadline for consortia to submit their technical and commercial proposals. Azerbaijan is expected to decide which project to prioritise before the end of 2011.

"We are convinced that Nabucco offers the best way to transport gas from Azerbaijan and other countries," Nabucco Managing Director Reinhard Mitschek said in a statement.

"Nabucco is Europe's flagship project for the Southern Corridor. It is cost-effective and competitive."

He said Nabucco's intergovernmental agreement and project support deals ensured backing for the pipeline.

Some analysts argue that Nabucco's aim of transporting up to 31 billion cubic metres (bcm) of gas a year is too ambitious and point to delays in the project timetable as a sign that it will not get off the ground.

Nabucco is backed by OMV, Germany's RWE, Hungary's MOL , Turkey's Botas, BEH of Bulgaria and Romania's Transgaz , and said on Friday that Germany's Bayerngas also intends to join.

The European Union supports Nabucco as a means of reducing the continent's reliance on Russian energy.

Azerbaijan's Shah Deniz II gas field, which is being developed by BP , Statoil and Azeri state oil firm SOCAR, is estimated to contain 1.2 trillion cubic metres of gas, which European companies hope can supply them for decades.

BP said on Tuesday, days before the deadline for bids, that it was mulling a fourth option in the form of a pipeline from Turkey to the Romanian-Hungarian border, amid doubts about the credibility of the pipeline plans already on the table.