(ShareCast News) - While some of the major oil-producing nations pussy-footed about in the spotlight of the OPEC meeting this week, three directors of oil investor Riverstone Energy again showed their confidence in the company´s prospects with a combined £0.59m share purchase as part of a continued buyback effort by directors to reduce the discount to net asset value at which the shares had been trading.David Leuschen and Pierre Lapeyre, Jr, industry veterans and two of the managing partners of US parent company Riverstone Holdings, plus Kenneth Ryan, a Riverstone partner who was appointed to the board of the UK-listed vehicle earlier this year, bought three parcels of 15,000 shares apiece in FTSE 250-listed Riverstone Energy at prices varying between 1,303p and 1,315p.Last week, the trio bought close to £1m worth in five batches either side of 1,300p, following seven other purchases since its third-quarter results were announced at the end of October.Riverstone Energy, a closed-ended investment company set up by Riverstone Holdings to invest in oil and gas exploration and production and midstream sectors, mainly through opportunities presented by the parent's energy investment platform, at the time reported a NAV of $1.56bn, or $18.41 per share."Today's results highlight REL's ability to navigate challenging commodity price environments and deliver value to shareholders," said chairman Richard Hayden said."The company's NAV per share [increased] 13% since June's results and 16% since December 2015."Furthermore, this does not reflect the uplift of REL's recent $175m investment in Centennial, which closed after the end of the quarter and is currently trading at a 45% premium to REL's cost base."Hayden said the board remained sensitive to the discount to NAV at which the REL shares were currently trading, and will continue to evaluate open market purchases as authorised by the shareholders at the AGM.Top Director BuysRiverstone Energy Limited (RSE)Director name: Lapeyre Jr.,Pierre FAmount purchased: 15,000 @ 1,315.15pValue: £197,272.50Riverstone Energy Limited (RSE)Director name: Leuschen,David MAmount purchased: 15,000 @ 1,308.99pValue: £196,348.50Riverstone Energy Limited (RSE)Director name: Ryan,KenAmount purchased: 15,000 @ 1,302.59pValue: £195,388.50Marston's (MARS)Director name: Glickman ,Catherine Amount purchased: 25,000 @ 132.81pValue: £33,201.35Babcock International Group (BAB)Director name: Martinelli ,Franco Amount purchased: 2,994 @ 934.91pValue: £27,991.14Marston's (MARS)Director name: Findlay,Ralph GrahamAmount purchased: 18,675 @ 133.13pValue: £24,862.03Marston's (MARS)Director name: Findlay,Ralph GrahamAmount purchased: 18,727 @ 132.76pValue: £24,861.97Octagonal (OCT)Director name: David Davison,Martin Amount purchased: 1,000,000 @ 2.05pValue: £20,500.00Avon Rubber (AVON)Director name: Ponsonby,ChloeAmount purchased: 1,000 @ 1,021.00pValue: £10,210.00Halma (HLMA)Director name: Barone Soares ,Daniela Amount purchased: 634 @ 939.32pValue: £5,955.28Octagonal (OCT)Director name: David Davison,Martin Amount purchased: 250,000 @ 2.00pValue: £5,000.00Halma (HLMA)Director name: Barone Soares ,Daniela Amount purchased: 520 @ 954.00pValue: £4,960.79Oxford Biomedica (OXB)Director name: Tallarigo ,Lorenzo Amount purchased: 75,417 @ 3.50pValue: £2,639.60Centrica (CNA)Director name: Valle,Margherita D.Amount purchased: 980 @ 202.90pValue: £1,988.42Octagonal (OCT)Director name: David Davison,Martin Amount purchased: 50,000 @ 2.00pValue: £1,000.00Standard Life (SL.)Director name: Matthews,PaulAmount purchased: 64 @ 352.60pValue: £225.66Standard Life (SL.)Director name: Savage,LukeAmount purchased: 43 @ 352.60pValue: £151.62Standard Life (SL.)Director name: Skeoch,KeithAmount purchased: 35 @ 352.60pValue: £123.41Top Director SellsLindsell Train Inv Trust (LTI)Director name: Landman,RoryAmount sold: 102 @ 86,500.00pValue: £88,230.00Lindsell Train Inv Trust (LTI)Director name: Landman,RoryAmount sold: 100 @ 86,500.00pValue: £86,500.00Digital Globe Services Ltd (di) (DGS)Director name: Flowers,DavidAmount sold: 46,532 @ 58.00pValue: £26,988.56