The company, led by Graham Stewart, said an independent asset valuation by oil consultants Gaffney, Cline & Associates valued its assets at between 186p and 225p, or $879 million (£690 million) and $1.1 billion, at the end of December. That was lower than a $1 billion to $1.2 billion valuation at the end of September when oil was around $80 a barrel.