William Knox D'Arcy (11 October 1849 – 1 May 1917) was a British-Australian businessman who was one of the principal founders of the oil and petrochemical industry in Persia (Iran).

The D’Arcy Concession was signed in 1901 and allowed D'Arcy to explore, obtain, and market oil, natural gas, asphalt, and ozokerite in Persia.

In 1889, with a substantial fortune, D'Arcy and his family moved to England, where he bought the Stanmore Hall mansion, Bylaugh Park, and a house on Grosvenor Square.

[6] Drilling in southern Persia at Shardin continued until 1907, when the search was switched to Masjed Soleyman (Masjed-e-Sulayman in Persian مسجد سلیمان), in a place named Maydon-e-Naftune.

In early May 1908, they sent Reynolds a telegram stating that they had run out of money and ordering him to "cease work, dismiss the staff, dismantle anything worth the cost of transporting to the coast for re-shipment, and come home".

[7] In April 1909, D'Arcy was appointed a director of the newly founded Anglo-Persian Oil Company (APOC),[6]: 148  which would later become British Petroleum (BP).

The financial support given by Burmah Oil and the British Admiralty meant that D'Arcy could no longer put his name to the new company despite the best efforts of his wife, and so was a shareholder.

[9] Then he commissioned from William Morris and Edward Burne-Jones a suite of tapestries, 'The Quest of the Holy Grail', that were displayed in the hall but are now dispersed.