United holds a 10% stake in the Colter discovery, which sits off England's south coast.
Colter is adjacent to Wytch Farm, the largest onshore oil field in Europe, where more than 450mln barrels of oil have been produced.
With the contract now signed, drilling operations can get underway as planned in the fourth quarter of this year.
Colter was discovered in 1986 by well 98/11-3 which encountered a 10.5 metre oil column in the Sherwood Sandstone.
The well will be drilled in an area updip of the existing discovery, targeting gross unrisked mid-case volumes of over 19mln barrels of recoverable oil.
“We are delighted that the rig contract has been finalised and operations at the Colter well are continuing to progress as planned,” said chief executive Brian Larkin.
“Colter is in an excellent location and we believe there to be significant potential in this play, which has yielded Europe's most prolific onshore field at Wytch Farm.”
As for the Podere Maiar well in Italy, plans to develop a 150,000 cubic metres of gas per day facility are well advanced, while a 3D seismic programme is proposed for early 2019 to progress additional targets within the licence.
UOG shares rose 2.9% to 5.4p on Friday.