"What I always worry about is the stories we should be watching, the unstable suppliers," Croft recently told CNBC's "Worldwide Exchange."
RBC has warned clients that 500,000 barrels per day could be periodically lost from the two nations, and elections may bring additional unrest.
Half a million bpd represents just half a percent of daily global demand, but a disruption of that scale would have an outsize impact given the anticipated loss of roughly 1 million barrels a day of Iranian crude in the coming months. Iran's exports are shrinking as oil buyers cut off purchases under threat of sanctions from the Trump administration.
"If you're going to have Venezuela continuing to decline, a million barrels of Iran off the market, you can't afford to lose another big, major producer," Croft said.
Washington is largely depending on Saudi Arabia, Russia and a handful of other producers to keep the market supplied and prevent an oil price spike as Iran's shipments dwindle. Traders recently sent Brent crude to nearly four-year highs above $86 a barrel, as fears that the Saudi alliance will fall short stoked concern about $100 oil.
Investment bank Barclays does not think oil prices will hit triple digits, but the outcome of Nigeria's elections in February presents the biggest risk to that outlook, Michael Cohen, the bank's head of energy markets research, said in a recent note to clients.
If Nigeria's political opposition unseats President Muhammadu Buhari, Barclays analysts believe the new leadership will probably have to renegotiate a deal with militants brokered by Buhari's government. During a political transition, militants might resume attacks on oil infrastructure, which caused Nigeria's output to plunge by about 400,000 bpd in early 2016.
Analysts at Barclays say there's a growing chance that the opposition can present a credible alternative to Buhari, whose popularity is waning and who spent much of his presidency seeking medical treatment overseas.
"Oil market participants ought to be more concerned about the possibility of disruptions in the Niger delta," Cohen wrote, referring to Nigeria's southern oil-producing region, a maze of waterways where militants staged daring attacks between 2006 and 2009 and again in recent years.
Oil theft also remains endemic in the Niger Delta. This month, a pipeline blast believed to be caused by petroleum thieves killed dozens, sparking protests among locals who blamed the Nigerian National Petroleum Corporation for the explosion.