United Oil & Gas dropped 10% as it cautioned that conditions for its sale of the Maria licence in the North Sea to Quattro Energy had not been met.
Longstop date for the deal was the end of July and discussions, described as advanced, are underway about a further possible extension.
Maria is a discovery in Block 15/18 in the UK Central North Sea Licence P2519.
Shares in United Oil fell 0.15p to 1.25p.