ONGC Videsh (OVL), the overseas arm of Oil and Natural Gas Corporation, will buy up to 33% stake in two Caspian sea blocks off Turkmenistan for Rs 150-200 crore."We have concluded a deal with Denmark's Maersk Oil and German oil and gas firm Wintershall for taking up to 33% stake in Block 11 and 12 in offshore Turkmenistan," R S Butola, managing director of OVL, said.Maersk Oil, with an 80% holding, is the operator of the blocks, which cover about 5,663 sq km, while Wintershall, a unit of the BASF chemicals group, owns the remaining 20% stake.Butola said OVL was likely to sign a deal within a month. "We are waiting for the approval by the Turkmenistan government. Once that is obtained, we will sign a production sharing contract," he said, adding the deal has been delayed due to the death of Turkmenistan's President Saparmurat Niyazov last month.