Shares in Falkland Islands oil and gas explorer Rockhopper Exploration have risen by 779% over the past year but two directors still believe they are worth buying. Executive chairman Dr Pierre Jungels and non-executive director Chris Walton have both added to their shareholdings the week after Rockhopper confirmed its oil discovery at its Sea Lion prospect was a medium grade crude. Dr Jungels invested £69,700 in 23,350 shares at 298.5p each, which takes his shareholding to 889,424 shares. This is the first purchase by Jungels since he bought 150,000 shares at 32p each in June 2009. Walton bought a further 8,300 shares at 297.625p each. His investment of £24,702 takes his shareholding to 32,109 shares. This is the first time that Walton has bought shares in more than two years. A sample from the Sea Lion 14/10-2 oil discovery well in the North Falkland Basin was tested under reservoir conditions and found to be a medium grade crude. "These positive results, when combined with our knowledge of reservoir quality from logging data, give us further comfort that a flow test of the Sea Lion well will confirm a mobile crude oil," Sam Moody, Rockhopper's managing director, commented on the day of the announcement. "The wax content is typical for a lacustrine sourced crude oil and significantly lower than many other producing oilfields worldwide. Furthermore the viscosity, gas oil ratio, FVF and sulphur are all better than we anticipated," he added. Last month, Rockhopper upgraded its estimate of recoverable reserves at the Sea Lion prospect in the North Falkland Basin from 170m barrels to 242m barrels, adding it has "significant upside potential".Dr Jungels was chief executive of Enterprise Oil between 1996 and 2001. Walton is a former finance director of easyJet. Top Director BuysTVC Holdings (TVCH) Director name: Mr Shane ReihillAmount purchased: 727,475 @ 45.79p Value: £333,111Rockhopper Exploration (RKH) Director name: Dr Pierre H JungelsAmount purchased: 23,350 @ 298.50p Value: £69,700Rockhopper Exploration (RKH) Director name: Mr J C WaltonAmount purchased: 8,300 @ 297.62p Value: £24,702Penna Consulting (PNA) Director name: Sir James Harvie-WattAmount purchased: 17,000 @ 115.00p Value: £19,550Mid Wynd International Inv Trust (MWY) Director name: Mr Russell Napier Amount purchased: 1,400 @ 963.50p Value: £13,489MS International (MSI) Director name: Mr Michael J BellAmount purchased: 10,000 @ 125.00p Value: £12,500Top Director SellsVT Group (VTG) Director name: Mr Paul J LesterAmount sold: 262,081 @ 792.00p Value: £2,075,682VT Group (VTG) Director name: Mr Paul J LesterAmount sold: 83,942 @ 795.00p Value: £667,339VT Group (VTG) Director name: Mr Philip HarrisonAmount sold: 49,378 @ 795.00p Value: £392,555VT Group (VTG) Director name: Mr Chris J CundyAmount sold: 42,933 @ 795.00p Value: £341,317General Electric (GEC) Director name: Mr John G. RiceAmount sold: 21,575 @ € 11.30 Value: € 243,703General Electric (GEC) Director name: Mr Michael A. NealAmount sold: 21,475 @ € 11.30 Value: € 242,573VT Group (VTG) Director name: Mr Matthew JowettAmount sold: 29,208 @ 795.00p Value: £232,204VT Group (VTG) Director name: Mr Paul J LesterAmount sold: 20,180 @ 795.00p Value: £160,431VT Group (VTG) Director name: Mr Chris J CundyAmount sold: 19,481 @ 795.00p Value: £154,874VT Group (VTG) Director name: Mr Chris J CundyAmount sold: 12,708 @ 792.00p Value: £100,647