US energy company Marathon Oil has agreed to sell its 18.5% stake in the Corrib gas field off the coast of Mayo in a deal which could be worth up to $400m (€285m).

The stake is being bought by Vermilion Energy Trust, an oil and gas company based in Canada. Vermilion will pay an initial $100m, with the rest being made when the first commercial gas is produced at Corrib. Vermilion says it expects first gas by the end of 2011.

Shell holds a 45% interest in the Corrib project, while Statoil Hydro has 36.5%. An Bord Pleanála is due to finish its oral hearing this week into Shell's application for a modified onshore pipeline route to bring the gas ashore.

Last year, Marathon sold another Irish subsidiary for $180m (€125m) to Star Energy, which is owned by Petronas, Malaysia's national oil company. Its assets included a 100% operated interest in the Kinsale Head Area comprising Kinsale Head, South West Kinsale and the Ballycotton gas fields, as well as an 86.5% interest in the Seven Heads gas field which is tied back to Kinsale.