"The rig modification programme is behind schedule and it is not going to be possible to get the barge out of Astrakhan before the end of this year," OKIOC spokesman Nick Wood told Reuters by telephone.

"Our plan is to have the rig ready and available to operate so that it can be moved onto the rig site as soon as the weather permits."

OKIOC has brought a rig mounted on a swamp barge, originally used in Nigeria, to the Caspian to develop the offshore fields. But before it can be used, it must be modified to cope with shallow water and ice pressure during the winter, and its living quarters need to be upgraded.

Wood said ice was currently preventing the barge from leaving the Russian Volga River Port of Astrakhan, but this could melt as early as March.

OKIOC unites U.S.-BasedPhillips Petroleum, Japan's Inpex, Italy's Agip, BG Plc, an alliance of BP and Statoil as well as Mobil, Shell and Total.

The consortium carried out a seismic survey on the North Caspian Sea in 1994-97 which showed the possible existence of large oil fields with an estimated four billion tonnes of hydrocarbon reserves. Wood said weak oil prices had not affected the consortium's commitment to the project. The oil price has slid 40 percent this year due to weakening demand, particularly in Asia's financially troubled "tiger" economies.