The remaining 24 crew were saved but some suffered "limited injuries" and a "search is ongoing for three others -- two Indians and a Bangladeshi," Aramco said in a statement emailed to AFP.
It said a thorough investigation into the incident would take place.
The platform sank in Safaniya, the world's largest offshore oilfield, in Eastern Province 265 kilometres north of Dhahran, home to the world's largest oil company in terms of production and reserves.
The company said today's incident would not affect overall production at the field.