On Nov. 5, the U.S. government is due to reimpose sanctions on Iran's exports of oil, and the uncertainty on the size and timing of the resulting production losses are supporting crude oil prices at their highest levels since 2014, Goldman Sachs analysts said.

Front-month Brent crude oil futures settled Oct. 4 trade on the New York Mercantile Exchange at $84.58 per barrel, well above the Goldman Sachs 2018 forecast peak of $82.50/bbl, Damien Courvalin said, acting as the lead analyst on an Oct. 4 commodities research note. December West Texas Intermediate crude oil futures closed the session at $74.33/bbl. Both contracts had retraced prior gains on reports of larger-than-anticipated builds to crude oil inventories.

The U.S. Energy Information Administration reported an 8 million-barrel build in U.S. crude oil inventories for the week to Sept. 28.

The first U.S. sanctions against OPEC-member Iran went into effect in early August but did not include Iran's oil exports. Goldman Sachs expects as much as 1.5 MMbbl/d of crude oil exports to be lost in November if sanctions are imposed.

In an Oct. 5 note, Jefferies analysts said Iranian exports could fall below 1 MMbbl/d in November.

Extra inventories created by a softening global balance in the second and third quarters should provide enough oil to meet demand, but earlier and larger declines than forecast will be harder for producers to offset, Courvalin said.

Jefferies analysts said global spare capacity is dwindling to the lowest level they can document. "Inventories are at normal levels, meaning any further supply disruptions would be difficult for the market to manage — and could lead to spiking crude oil prices," the analysts said.

While Goldman Sachs sees near-term market support, the longer-range uptrend could be stifled as new spare capacity comes online and with fundamental data outside of Iran having "not turned bullish in our view."

"We expect fundamentals to gradually become binding by early 2019 as new spare capacity comes online ... pointing to the global market eventually returning into a modest surplus in early 2019," the Goldman analysts said.