In a second test of the Upper Kimmeridge limestone zone, carried out on March 1, the well flowed at an instantaneous rate above 1,000 barrels of oil per day before settling down to an average rate of 838 bopd over a 7.5 hour period.
The well has now been shut-in for a 12-hour pressure build up test.
Once testing of the Upper Kimmeridge is complete, the programme will move up to evaluate the separate Portland sandstone reservoir.
"The well continues to perform above management's expectations,” said Stephen Sanderson, UKOG chief executive. “We look forward to testing the overlying Portland shortly."
Neil Ritson, Solo Oil chief executive, meanwhile said: "The Horse Hill well is showing excellent characteristics and the data collected will be invaluable in designing a development scheme.
“We look forward to news of the Portland sandstone test which is now planned."
UKOG owns a 19.96% interest in the Horse Hill project, while Solo Oil has a 6.5% stake.
The other stakeholders in the project include Alba Minerals (LON:ALBA), which has 9.75%, as well as Stellar Resources (LON:STG) and Doriemus (LON:DOR) which each have 6.5% and Evocutis (LON:EVO) with 1.3%.