For two decades, specialising in gold and tin, he worked as a mining engineer all over the world – Australia, China, Russia, Malaya, Mexico, Uruguay and Nigeria.
In his efforts to source food and supplies for the British Army in Mesopotamia (today's Iraq), Holmes travelled widely through the Middle East and may have heard rumours of a possible oil seepage on the eastern seaboard of the Arabian peninsula.
[2] In 1920, Holmes helped set up the Eastern and General Syndicate Ltd in London to develop, among other things, oil ventures in the Middle East.
With Ibn Saud's permission, he carried out a survey over four weeks in the desert and returned to Hofuf with earth samples which he claimed bore traces of oil.
In order to allay the suspicions of British officials, Holmes claimed that he was looking for a rare butterfly, the Black Admiral of Qatif, although this deception appears not to have been effective.
But when a subsequent survey was unfavourable, and a financially challenged Eastern and General Syndicate failed to find a bidder, the concession for al-Hasa was allowed to lapse.
When Ibn Saud's adviser, the former British colonial officer Harry St. John Philby, got wind of his arrival he attempted to deter Holmes from joining the negotiations by informing him that he was persona non grata in Jeddah and was remembered for the failure to exploit the first al-Hasa concession.
"Holmes does not seem to share the otherwise universally held belief that Ibn Saud regards him unfavourably," wrote the IPC representative, Stephen Hemsley Longrigg.
After three days, during which time he met with Saudi finance minister Abdullah Suleiman, Holmes left Jeddah and took no part in the al-Hasa negotiations.
On 23 December 1934 Sheikh Ahmad signed an oil concession (covering the entire 15,800 square km of Kuwait for 75 years) to this new company and appointed Major Holmes as his representative in London.
[10] Described as being "of powerful physique, of blunt speech and great strength of character",[11] Holmes possessed qualities of charm and generosity that won him the admiration of Arabs across the region.