Oil and gas explorer PetroNeft Resources had a major breakthrough after finding a new oil field at Sibkrayevskaya in Licence 61 in Russia, which it considers to be its largest single discovery to date. Based on preliminary analysis, the company noted that the oil is of "good quality" consistent with other fields in Licence 61 and said it estimates that the ultimate recoverable reserves in the field could be "significantly larger than the 44m barrels pre-drill target defined by Ryder Scott for the prospect."This discovery well adds a sixth oil field to Licence 61 and proves the strategy of following up on re-interpreted well logs from old wells that show potential by-passed oil pay zones, the company said in its statement. Shares of the Russia-focused oil explorer jumped 17% to 38p in morning trading in London.AR