There may be as much as 1.5 billion barrels of reserves in frontier prospects off the coast of Ireland, junior explorer Europa Oil & Gas said.

Europa holds a minority stake in the Porcupine frontier license off the western Irish coast alongside operator Kosmos Energy. Europa, which has headquarters in London, said a third-party assessment of preliminary data found prospective resources of 1.49 billion barrels of oil equivalent in the region.

"These are very significant volumes of hydrocarbons," Europa Chief Executive Officer Hugh Mackay said in a statement. "Europa considers the prospects to be at drillable prospect status and we will update the markets when the operator Kosmos provides more clarity with respect to drilling plans."

Kosmos acquired an interest in offshore Ireland in 2013. The company had no update on drilling operations. Europa said if a decision is made to expand operations in the Porcupine prospect, Kosmos will incur the entire costs of the first exploration well.

The Irish government is hedging its bets on the reserve potential. Three years ago, the government said offshore reserves produced 14 billion cubic feet of natural gas and no oil.

Ireland imports all of its oil and relies in foreign sources for 90 percent of its natural gas needs.

The government last year said it's seeing industry interest for a 2015 auction for additional offshore acreage.