The British-based energy firm, which currently has no producing assets, said on Monday it had found oil at its SNE-1 well around 100 kilometres off the coast of the west African country.
The well, located near its FAN-1 well where it found oil last month, could hold 150-670 million barrels of recoverable resources, Cairn said about its preliminary estimates.
Analysts said the two successful oil discoveries could provide Cairn with an option to sell parts of its 40 percent stake to raise cash for its 2015 exploration work in northwest Europe and Morocco.
Cairn is the operator and 40-percent owner of three blocks off the coast of Senegal, while other stakeholders include oil major ConocoPhillips (COP.N), which owns 35 percent.
The oil explorer has been unable to tap its $1 billion stake in Cairn India, a business whose backdated taxation practices are being investigated by Indian authorities.
Shares in Cairn were up 9 percent at 172 pence by 0849 GMT.
(Reporting by Karolin Schaps, editing by Louise Heavens)