Talks about a merger involving Tullow Oil, the London-listed African oil explorer, and Meren Energy, a Canadian-listed peer, have collapsed.
Sky News has learnt that discussions about a tie-up were progressing as recently as this month but are now said to have been terminated.
It was unclear on Tuesday evening what the reason was for the abandonment of the negotiations.
Tullow Oil, which has a market valuation of about £275m, is focused on West-African producing assets in Ghana, Gabon and the Ivory Coast.
The company has seen its stock plunge dramatically since its peak valuation of about £15bn.
Last December, it saw merger talks involving Kosmos Energy fall apart.
Listen to The World with Richard Engel and Yalda Hakim every Wednesday
Tap to follow
Meren Energy, which until recently was called Africa Oil Corp, is substantially larger than Tullow Oil in valuation terms.
Listed in Canada and Sweden, it has a market capitalisation equivalent to approximately £980m.
Run by chief executive Roger Tucker, Meren recently said it had up to $500m to spend on acquiring producing assets in Africa.
A spokesman for Tullow Oil declined to comment.
