Rui de Sousa, the long-running Non-Executive Chairman of SOCO International, has raised his stake through the purchase of 50,000 shares, taking advantage of the recent slump in the oil and gas explorer's share price.De Sousa, who has been on the board of the FTSE 250 firm since 1999, snapped up the 0.02% holding at a price of 400p a share, spending £200,000.The transaction, announced on Monday, lifted his total interest in SOCO to around 9.11m shares, representing a 2.75% holding.After hitting a 52-week closing high of 474.8p in early March, SOCO's stock has since slumped nearly 17%. The company revealed its annual results on March 5th which showed that revenues and operating profits in 2013 declined from record highs the previous year.Top Director BuysSoco International (SIA) Director name: Mr Rui C De SousaAmount purchased: 50,000 @ 400.00p Value: £200,000Global Petroleum Ltd. (GBP) Director name: Mr Peter HillAmount purchased: 530,000 @ 6.46p Value: £34,238Fulcrum Utility Services Ltd. (DI) (FCRM) Director name: Mr Phil HolderAmount purchased: 350,000 @ 7.18p Value: £25,130Shanks Group (SKS) Director name: Dr Stephen RileyAmount purchased: 20,000 @ 116.50p Value: £23,300PZ Cussons (PZC) Director name: Mr Richard J HarveyAmount purchased: 3,522 @ 351.40p Value: £12,376BC