Irish gas company Enterprise Energy Ireland still intends to drill for oil on Lough Corrib.
The announcement is despite a European Commission ruling which prevents them from merging with American and Norwegian companies.
The three companies had sought the go-ahead to jointly market gas from the Lough Corrib gas field off the West coast.
Their appliction to the EU has been refused, undrer the basis that customers should have more choice over who they buy gas from.