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.