Tullow Oil has increased the size of its Jubilee oil field offshore Ghana, extending it eastwards with the Mahogany-4 well.

ExxonMobil and China National Offshore Oil Company are bidding for the field and, while Tullow kept reserve figures the same, analysts have said that the news could increase current estimates of the recoverable amount.

It has been suggested that the barrel mid-range reserve estimate could as much as double to 1,200 million.

Tullow has to complete estimates on two further appraisal wells in the field, after which time it could alter its reserve.