U.S. sanctions on Iranian crude could soon push oil prices above $90 a barrel, one analyst told CNBC ahead of the penalties snapping back into place.
"As we go more towards (the fourth quarter) … that's when we really see the risk of prices going well into the 80s and potentially even into the 90s but very critical is how much Iranian production we lose," Amrita Sen, chief oil analyst at Energy Aspects, told CNBC's "Squawk Box Europe" on Monday.
"A lot of people think China can just buy all of the Iranian oil but they came out and said: 'Yes, we may not reduce but we are not going to increase our intake either.' So, you could see a significant crunch in terms of lost supplies into the market and then that obviously means higher prices," she added.
Investors are seen weighing bullish factors that include potential supply disruptions to Iranian crude exports against more bearish indicators, such as a ramp-up in production by OPEC and its allied partners.
Alongside Russia, OPEC kingpin Saudi Arabia and other members of the Middle-East dominated oil cartel agreed in late June to begin increasing production by up to 1 million barrels per day starting in August.
The decision has helped to put a lid on a price rally, with crude futures falling more than 7 percent since climbing above $80 a barrel in May.
Against that backdrop, some analysts don't see prices moving as sharply.
Although markets will remain tight in the short term, extra production from Saudi Arabia and others in the fourth quarter is expected to cap price rises going forward, Sushant Gupta, research director for Asia refining at Wood Mackenzie, told CNBC's "Squawk Box." He said prices should be supported at around $75 for now.
Together with expectations of slower global oil demand growth next year, the factors were indicative of a loosening in the oil markets towards the fourth quarter of the year and going into 2019, Gupta said.
Crude sanctions
Brent crude, the international benchmark, was trading around 0.35 percent higher at $74.01 on Tuesday, while West Texas Intermediate futures rose 0.13 percent to trade at $69.10.
The price jump earlier this summer came about in large part because of President Donald Trump's decision to pull the U.S. out of an international agreement to curb Iran's nuclear program. The move is widely expected to severely hinder the world's fifth-largest oil producer, with the re-imposition of U.S. crude sanctions on November 4 set to follow economic sanctions due to take effect from Tuesday.
The last time Iran was sanctioned, about half its current oil exports of some 2.4 million barrels were removed from the market. However, this time around, many energy analysts believe sanctions will remove far less, maybe around half the prior amount, but some onlookers have recently raised their expectations amid signs some companies are complying with tough talk from the White House.
Morgan Stanley, for instance, now expects Iranian production to drop to 2.7 million barrels a day by the fourth quarter, with more than 1 million barrels taken offline.
Energy Aspects' Sen said that even predictions of Iran's crude production falling by much as 1.5 million barrels a day could prove to be "conservative" by year-end, particularly because of escalating tensions between Washington and Tehran.
Meanwhile, analysts at Bank of American Merrill Lynch said in a research note published late July that "for every 1 million barrels per day imbalance, we see a price impact on Brent of around $17."
— CNBC's Patti Domm and Cheang Ming contributed to this report.