Solo Oil, one of the partners of the Horse Hill-1 well in the northern Weald Basin, has medium case-estimated the "Portland oil discovery" could host 3.1 million barrels of gross in place hydrocarbons within the upper Portland sandstone.

Solo said an additional 16.8 MMbls of gross unrisked in-place oil was in a separate, deeper sand in the Portland interval within an untested fault block to the south.

"As previously announced, the well is being deepened to the Triassic [sandstone] where an additional target, believed to have potential for gas, is expected to be reached in the next two weeks," Solo said.

The Portland sandstone is a producing reservoir at the nearby Brockham oil field.

Solo owns a 10% interest in Horse Hill Development Limited which is the operator (65%) of the well's permit PEDL137 and neighbouring PEDL246.

Magellan Petroleum Corporation owns the remaining 35% stakes in the blocks.