Saudi Aramco, the state-owned firm of the world's largest oil exporter, said on Sunday its downstream investments would exceed $100 billion over the next decade, as global demand for oil rises by a quarter in the next 25 years.

"Globally, these investments will exceed $100 billion over the next decade alone and that is premised on our belief in the long term sustainability of oil demand," Khalid al-Falih, the company's chief executive said at a petrochemicals conference in Bahrain.

"As a result of both global demographic growth and rising standards of living in the developing world, we see global demand for oil growing by a quarter over the next 25 years," he said.

Falih said Aramco's refining capacity would be between 8 million to 10 million barrels a day (bpd) in the coming years, a figure exceeding the goal cited by Aramco in 2012 of 8 million bpd.

"In the years to come, Saudi Aramco will have 8 to 10 million bpd of participate refining capacity primarily in the high-demand growth markets of the Far East and of course here at home in the Middle East that will make us one of the largest downstream players on the planet by volume," Falih said.

According to the company's 2013 annual review, Aramco and its subsidiaries own or have equity interest in domestic and international refineries with a total worldwide refining capacity of 4.9 million bpd, of which its equity share is 2.6 million bpd, making it the world's sixth-largest refiner.

Aramco is also looking to grow within the petrochemicals sector with two major projects.

Aramco has a joint venture with Dow Chemical Co to build the $20 billion Sadara petrochemical complex in Jubail that is due to come on stream in the second half of 2015 is also expanding its petrochemical complex called PetroRabigh that it jointly owns with Sumitomo Chemical

"That will take our total chemicals participate production capacity to more than 15 million tonnes per year," Falih said.