Saudi Aramco's chief exec has warned of a "worrying" shortage in long-term oil supply as financial investment dries up.
Speaking at a conference in Istanbul, Amin Nasser said it was too early to tell whether shale oil exploration would be sufficient to replace developed mainstream oil and gas extraction.
"If we look at the long-term situation of oil supplies, for example, the picture is becoming increasingly worrying," said Nasser.
Financial investors are shying away from making much needed large investments in oil exploration, long-term development and the related infrastructure.
Investments in smaller increments such as shale oil will just not cut it.
He continued: "New discoveries are also on a major downward trend. The volume of conventional oil discovered around the world over the past four years has more than halved compared with the previous four."
Aramco is preparing to sell around five per cent of itself next year in an initial public offering. It is investing in maintaining its oil production capacity of 12m barrels per day.
"We plan to invest more than $300bn (£233bn) over the coming decade to reinforce our pre-eminent position in oil, maintain our spare oil production capacity, and pursue a large exploration and production programme centreing on conventional and unconventional gas resources," said Nasser.