The first potential shock Croft and her team at RBC are monitoring is a debt default by Venezuelan oil giant Petroleos de Venezuela SA. Oil production from the state-owned PDVSA has steadily slipped as the country grapples with a financial crisis after the collapse in crude prices in 2014 and years of economic mismanagement, CNBC reported.
"They have $3.5 billion in national oil company debt coming due in October-November. If they default, that could be significant for Venezuela's production outlook," Croft told CNBC's "Squawk on the Street" on Tuesday.
Lower crude production from Venezuela would tend to support the oil market, which has been oversupplied for years.
The second surprise would come if the United States abandons an international deal that lifted sanctions on Iran. President Donald Trumpcould refuse to certify that Iran is complying with an accord that puts limits on its nuclear program. That could lead to the renewal of sanctions, which could impact Iran's oil production.
John Kilduff, founding partner at energy hedge fund Again Capital, said these geopolitical concerns may be somewhat overstated. He noted that the five other nations that negotiated the Iran nuclear deal would probably break with the U.S. and refuse to snap sanctions back on Iran.
He also noted that Venezuela is indebted to Russia and China. Russian oil giant Rosneft has amassed a large stake in PDVSA's U.S.-based refiner Citgo by bankrolling Venezuela. China has long lent Venezuela money in exchange for oil.
However, Rosneft has recently suggested it is done lending to PDVSA, which has less than $10 billion left in reserves, according to Croft.
"The math simply does not work on PDVSA staying solvent" without help from Russia and China, she said. "So we think this default is a clear and present danger."