Shares in Regal Petroleum bombed today following "poorer than anticipated" production and the resignation of the chief executive David Greer.The UK oil and gas explorer currently at work in Ukraine dropped 27% today and are down about 80% this year. Keith Henry, current chairman of Regal will assume Greer's daily responsibilities until further notice. Revenue rose to $15.9m in the half year to June, up 84% from the same period the year before. The company also posted a profit of $3.4m, from a loss of $6.0m previously. But the results were not as good as hoped due to lower than expected production. In a separate operational update statement on MEX-120, Regal noted that "production rates are showing a decreasing trend that has not yet stabilised", and are undertaking a strategic review of reservoir performance.The company continues to be hampered by the Ukrainian Ministry of Environmental Protection which has questioned Regal's compliance with certain legislation in Ukraine.It has also sold to Chevron its 100% owned Barlad concession in Romania for a cash consideration of $25m.