Investing.com - President Trump's efforts to get Saudi Arabia to produce more crude oil may be about more than simply its price in the marketplace.Analysts say Trump wants to make sure there is adequate supply to replace whatever production is lost from Iran, when economic sanctions kick in later this year. Iran was producing about 2.5 million barrels at its peak this year. There's also the need to compensate for Venezuela's continued production decline.Oil market experts say Saudi Arabia and Russia alone are incapable of replacing all of Iran's production, if that becomes necessary. They say Saudi Arabia might be able to supply an additional 700,000 barrels a day on a sustainable basis.That's far from the 2 million barrels a day mentioned in the President's tweet. Meanwhile, Russia is capable of a 400,000-barrel-a-day increase, they say.Analysts say Saudi Arabia has reason to cooperate with the U.S. because it has long considered Iran a rival in the Persian Gulf. Russia, however, may only cooperate if increasing production supports its price goals.