The German company said in a statement work began in Block Ta10 inland in Mauritania to explore the hydrocarbon potential in the area.
RWE said seismic surveys of the area were concluded most recently in 2010. Senior Vice President for Exploration Werner Schwarzhans said the reserve area was still considered frontier territory.
"We are very pleased that together with our partner [Repsol], we have commenced this well, which is both challenging from an engineering point as well as being of great interest in geological terms," he said in a statement.
RWE provided no estimate of the reserve potential in Mauritania. There was no statement from Repsol on the operations.
The U.S. Energy Information Agency ranks Mauritania 73rd in the world in terms of crude oil production.
Last year, German energy company Wintershall handed control of two onshore licenses back to the Mauritanian government because they weren't considered commercial prospects.
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