Shares in Northern Petroleum plunged on Tuesday, after the oil and gas explorer said it was undergoing a technical review and it was working to achieve extra cost efficiencies.The London-listed company, whose current daily production capacity at a developing prospect in Canada stands at 500 barrels, said that as part of its cost-cutting strategy it was undertaking "significant" reductions in administrative and corporate overheads."The first quarter of 2015 has been spent reorganising the company and its operations in Canada in response to the prevailing industry environment," said chief executive Keith Bush, adding that Stewart Gibson will leave his role as non-executive director.Bush said the company's focus for 2015 was to increase economic production in Canada and to invest in the group's assets in Italy, where its portfolio was recently boosted by a tie-up with Shell at the Cascina Alberto project, with a programme now due to start.Meanwhile, Northern Petroleum added that it had begun work in the Sicily Channel alongside Schlumberger and GEPlan, while process for the approval of an environmental impact assessment for a project in Southern Adriatic was underway.Northern Petroleum shares were down 13.85% to 4.20p at 11:39 on Tuesday.