Aberdeen oil firm Siccar Point Energy has started drilling a final appraisal well on the Cambo field, north-west of Shetland.
The Cambo field, which lies around 75miles north-west of Shetland, contains at least 600million barrels of oil, according to Siccar.
Results of the appraisal well are expected in the summer.
Meanwhile, the company has confirmed it has completed a sale of various working interests in the Greater Cambo Area to Shell.