Non-executive director George David has taken advantage of a fall in BP's share price to buy more shares in the company.He took 40,000 American Depositary Receipts (the equivalent of 240,000 shares) taking 20,000 at $35.55 (£23.04) a time and 20,000 at $35.45 a time.The shares have fallen sharply in line with a tumbling oil price since May, when David bought 30,000 ADSs, paying $43.99 each for half and $43.98 for the other half. David, an American, joined BP in 2008. He is a member of the chairman's, the audit, the Gulf of Mexico and the remuneration committees. He has previously worked with management consultant The Boston Consulting Group and elevator manufacturer Otis. Following Otis's merger with UTC in 1977, he moved up the ranks, becoming chief executive in 1994 and chairman in 1997, before he retired in 2009. Top Director BuysBP (BP.) Director name: Mr George DavidAmount purchased: 120,000 @ 386.14p Value: £463,368BP (BP.) Director name: Mr George DavidAmount purchased: 120,000 @ 385.06p Value: £462,072London Mining (LOND) Director name: Mr Luciano Ramos Amount purchased: 50,000 @ 343.00p Value: £171,500Fidessa Group (FDSA) Director name: Mr John HamerAmount purchased: 5,000 @ 1,530.00p Value: £76,500Energetix Group (EGX) Director name: Ms Clare SpottiswoodeAmount purchased: 167,000 @ 28.50p Value: £47,595Energetix Group (EGX) Director name: Mr Adrian HutchingsAmount purchased: 69,500 @ 28.50p Value: £19,808Meggitt (MGGT) Director name: Ms Brenda ReichelderferAmount purchased: 6,000 @ 328.89p Value: £19,733GLOBO (GBO) Director name: Mr Konstantinos (Costis) PapadimitrakopoulosAmount purchased: 105,000 @ 18.75p Value: £19,688Standard Life (SL.) Director name: Mr David Thomas NishAmount purchased: 6,000 @ 193.90p Value: £11,634