London — Oil prices rose on Tuesday as more evidence emerged that crude exports from Iran, oil cartel Opec's third-largest producer, are declining before the imposition of new US sanctions and as a hurricane moved across the Gulf of Mexico.

Benchmark Brent crude was up 55c at $84.46 a barrel by 7.30am GMT, having fallen as low as $82.66 on Monday. Brent hit a four-year high of $86.74 last week. US light crude was up 45c at $74.74.

Iran’s crude exports fell further in the first week of October, according to tanker data and an industry source, as buyers sought alternatives ahead of US sanctions that take effect on November 4.

The Islamic Republic exported 1.1-million barrels per day (bpd) of crude in that seven-day period, Refinitiv Eikon data showed. An industry source who also tracks exports said October shipments were, so far, below 1-million bpd.

This is down from at least 2.5-million bpd in April, before US President Donald Trump withdrew the US from a 2015 nuclear deal with Iran and re-imposed sanctions in May. The figure also marks a further fall from 1.6-million bpd in September.

Saudi Arabia, the biggest producer in Opec, said last week that it would increase crude output next month to 10.7-million bpd, a record. “Iranian barrels are declining fast, and Saudi Arabia’s promise to balance will face a reality check in a month’s time,” JP Morgan analysts said in a note.

Iranian oil minister Bijan Zanganeh on Monday called a Saudi claim that the kingdom could replace Iran’s crude exports “nonsense”.

Meanwhile, oil companies operating in the Gulf of Mexico shut down nearly 20% of oil production as Hurricane Michael moved towards eastern Gulf states including Florida. Forecasters predict the storm will become a Category 3 hurricane with sustained winds of 178km/h to 208km/h) and bring heavy seas to producing areas.

If forecasts prove accurate, the hurricane will largely miss major oil-producing assets in the Gulf, analysts said, but a change of track could widen the impact.

On Tuesday, the International Monetary Fund (IMF) cut its global economic growth forecasts for 2018 and 2019, saying trade tensions and rising import tariffs were taking a toll on commerce while emerging markets struggle with tighter financial conditions and capital outflows.