Jadestone Energy PLC (AIM:JSE) tumbled 33% as more technical problems saw its Montara field, offshore Australia, shut down again.
A gas alarm was triggered in a water ballast tank over the weekend, Jadestone said, indicating a possible seepage into adjacent tanks on the floating production vessel at the site.
The tank will be cleaned over the next week to identify any issues and carry out repairs.
Montara only came back on stream again in March after repairs to a cracked storage tank and problems in 4S, the water ballast tank that has caused this latest shutdown.
A year ago, Montara was responsible for half of Jadestone’s production of 15,000 barrels daily.
Paul Blakeley, chief executive, said: "While disappointing and frustrating to have to shut in Montara again, we will find and repair any additional defect while continuing with the overall planned programme of inspection of the storage tanks on the FPSO.”
Jadestone has net cash currently of US$7.1mln, said the statement.
Shares fell 11.5p to 23.5p.