United Kingdom publications such as The Financial Times, Times online and Thomson Financial all pointed to Santos as a likely predator, alongside bigger names like Royal Dutch Shell and Italy's Eni SPA.

But Premier's chief executive Simon Lockett has reportedly declined to comment over whether his company has received a takeover offer.

The $1 billion company is considered an attractive takeover target due to its broad exploration portfolio that spans from the North Sea to Mauritania, Vietnam and Indonesia.

With its eye on expansion, Santos pulled out of the United States earlier this year to concentrate on Asia, where Premier is said to have some of its best prospects.

Santos has also received a nod from the South Australian Government to remove its 15% individual shareholding cap, which could make it easier for the Adelaide-based major to raise capital for acquisitions and takeovers.

The companies are partners in Block 12E in Vietnam's Nam Con Son Basin, where Premier as operator made what appears to be a significant oil discovery at its Blackbird prospect a year ago.

Premier, which is also an 8.12% stakeholder in the troubled Chinguetti oil project, has been in takeover talks before. The company ended discussions with an unnamed bidder, believed to be Dubai Energy, in December.