US West Texas Intermediate (WTI) crude fell 0.20%, or 14 cents, to US$69.71 a barrel.
Crushing U.S. oil sanctions on Iran will resume in early November and already, American allies in Asia are cutting back on their purchases of Iranian crude.
Also weighing on oil prices, USA drillers added two oil rigs in the week to December 1, bringing the total count up to 749, the highest since September, Baker Hughes energy services firm said on Friday.
The Organization of the Petroleum Exporting Countries and other producers including Russian Federation meet on September 23 in Algeria to discuss how to allocate supply increases within their quota framework to offset the loss of Iranian supply.
US stock indexes broadly fell on Monday, weighing on oil futures, on expectations that the Trump administration would go ahead with the new tariffs and that Beijing would retaliate. Russia, the world's largest oil producer, and other producers in OPEC have kept in place a supply agreement to maintain prices while at the same time providing enough oil to the market.
Asked whether a deal between OPEC and other producers, a group known as OPEC+, could discuss increasing output from levels agreed in June, Novak said: "I think we have the possibility to discuss any possible scenarios".
Prices rose on Tuesday amid media reports that Saudi Arabia, the world's largest oil exporter, was comfortable with prices climbing above $80 a barrel.More news: Mourinho to be without five players for Wolves clash
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Crude posted a third weekly advance out of four as Iranian sanctions take center stage, with investors eyeing the impact on supply.
There are signs, however, that Saudi Arabian exports did not increase in July.
Oil futures also drew support from geopolitical risk on Tuesday.
Oil markets fell on Tuesday as the latest escalation in the Sino-U.S. trade war clouded the outlook for crude demand from the two countries, which are the world's top two oil consumers.
Russia, which is not a member state of OPEC, raised its production by 250 thousand barrels per day in May and can increase the supply by about 300 thousand barrels per day. The move was in retaliation for President Donald Trump's planned levies on $200 billion worth of Chinese goods.
Beijing on Tuesday quickly added US$60 billion of U.S. products to its import tariff list in retaliation for President Donald Trump's planned levies on US$200 billion worth of Chinese goods.
"The brinkmanship between Beijing and Washington has the potential to severely impact the competitiveness of USA crude oil and petroleum products in the Chinese market, and it will also deter Chinese investment in the US energy sector", said Abhishek Kumar, senior energy analyst at Interfax Energy in London.