Oil and gas exploration firm, Sirius Petroleum, recorded a big jump in losses but news of potential oil field targets buoyed shares.The company posted losses of $10.3m in the six months to the end of June, giving a loss per share of 1.63c.Sirius' figures showed a loss of $828,000 in the first five months of 2010.It said the results represented the costs of developing its strategy, reviewing potential marginal field opportunities and setting the structure for its oil trading activities. It added that cash costs incurred in the half year amounted to $4,785,000, which included the cost of pulling out of a deal to operate Nigeria's Ke oil field and the company's re-admission to AIM as an investing company."The vast majority of these costs are non-recurring in nature with normal overheads, net of sundry income amounting to $804,000,which is in line with expectations," the firm said.Sirius chairman Jack Pryde said the firm had its eye on "a number of attractive oil field assets" and was working to determine the economics of each project. "We will make an announcement as appropriate once we have selected our preferred first target and entered into an agreement to develop the asset," he said.Pryde added that the firm intended to ramp up its oil trading business and to import cargos of "increasing size and on a more frequent basis to generate a reliable income stream".This positive outlook reassured investors and shares rose 5% in early trading on Monday.