* OMV sells 9 pct in Nabucco to GDF SUEZ
* Stake was previously held by RWE
* Decision between Nabucco and TAP due in June (Adds Nabucco comment, shares, background)
VIENNA, May 28 (Reuters) - OMV AG has sold a stake of around 9 percent in the Nabucco West gas pipeline project to French group GDF SUEZ, bringing in a western European partner ahead of a decision due next month on whether the pipeline will be built.
The transaction follows OMV's move to acquire the stake from Germany's RWE, in a shareholder structure that has changed as the project to bring gas from Azerbaijan's Shah Deniz II field to Europe has been downsized.
The Shah Deniz consortium, led by BP and Azeri state energy firm Socar, has said it will decide next month whether to select Nabucco West or the rival Trans Adriatic Pipeline (TAP) project to transport its gas to Europe.
The building of a pipeline is key to Europe's reducing its dependence on Russian gas, and also to Azerbaijan's aim of diversifying its markets.
OMV gave no financial details for the GDF deal, which it said was subject to certain conditions and was expected to take place in the second half of this year.
Nabucco Chief Executive Reinhard Mitschek said on Tuesday: "The entry of GDF Suez strengthens the shareholder structure of Nabucco significantly and paves the way to the French market."
"The industry expertise of GDF Suez as the operator of the largest gas transport network in Europe and their status as the second-largest buyer of natural gas in Europe are of immense advantage to the project," he said.
"GDF Suez is already very active in the Nabucco countries."
Partners in Nabucco West, which would run from Turkey through Bulgaria, Romania and Hungary to Austria, now include BEH of Bulgaria, Turkey's BOTAS, FGSZ of Hungary, GDF SUEZ, OMV and Transgaz of Romania.
Shareholders in TAP, whose shorter route goes through Greece and Albania to southern Italy under the sea, are Norway's Statoil, Switzerland's AXPO and Germany's E.ON Ruhrgas. (Reporting by Michael Shields and Georgina Prodhan; editing by Patrick Graham)