Wessex rose on Thursday after it said drilling had started at a well off the coast of French Guiana in which it has a small stake.
The firm said the GM-ES-3 well was spudded by operator Shell on 29th December.
Wessex, through holding 50% of Northpet Investments, owns a net 1.25% interest in the offshore exploration licence 'Guyane Maritime'.
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Wessex's chief partners are Shell, which owns 45%, Tullow with 27.5%, and Total with 25%.
Chairman Malcolm Butler said this was the second well in the four well programme to assess the potential of the deep waters offshore French Guiana as a new oil province.
Wessex's shares were up 5% by 1500 following the announcement.
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