Four EU countries and Turkey have signed additional deals for the construction of the long-delayed Nabucco gas pipeline.
The ambitious and costly project will bring gas from central Asia to Europe, bypassing Russia and Ukraine, where rows over prices have disrupted supplies in the past
Officials from Austria, Bulgaria, Hungary and Romania gather in the central Turkish town of Kayseri for the signing which was to finalise the legal framework for the project.
Costing an estimated eight billion euros, the 3,300-kilometre pipeline was originally expected to become operational in 2014, but that has been pushed back to 2017.
Work is not due to start until 2013.
Gas is expected to come from Azerbaijan and possibly Turkmenistan, Iraq and Egypt.