The Strategic Petroleum Reserve 'would be harder to use,' and the only buffer for oil markets is Middle East production, energy expert says

• The SPR "would be harder to use" to balance a spike in oil prices, energy expert Dan Yergin said.
• The S&P Global vice chairman said that oil prices can spike if the Israel-Hamas war escalates.
• The only spare capacity right now is in the Middle East, in countries like Saudi Arabia.

The biggest tool the US uses to fight wild swings in oil prices may not be in play again as crude markets face the prospect of more geopolitical instability.

S&P Global Vice Chairman Dan Yergin, an energy expert and historian, told CNBC on Monday that the Strategic Petroleum Reserve is almost at the point where it's past the comfort level. 

"We've used about half of it, so it would be harder to use it," he said. "And we're kind of getting to a level where you don't want to use it."