Oil may not have been on China's official tariff list, but the country appears to have not imported any U.S. crude in August, according to Bimco's chief shipping analyst, Peter Sand, who cited U.S. Census data.
Bimco is the world's largest shipowners association with members in more than 120 countries that control around 65 percent of international tonnage.
According to Sand's research, Chinese imports accounted for 23 percent of total U.S. crude exports in 2017 and were averaging 22 percent for this year, up until August.
"In the first seven months of 2018 China imported an averaged 10.6 million barrels," Sand said.
August was "a massive change to the export pattern seen since early 2017. Chinese buyers, led by the world's top tanker charter Unipec, were rumored to have stayed away and this new data proves it."
Sand told CNBC: "China is keeping its oil import data closer than ever before. Up until March we had a good idea of where they were getting crude and that has all stopped. Now China is only releasing their import volumes. Not the sources of their imports."
According to Sand's research, China in August and September replaced its oil exports with West African crude from Nigeria and Angola.
"China can replace their U.S. oil exports with West African crude if they wanted," said Sand. "We have gotten no indications if Western Africa is reaching their limit. This was the crude the U.S. used to buy before the shale revolution."
For the oil tanker market, distances of the shipments matter more than volumes.
"Very large Crude carriers (VLCC) and Suezmax tankers can charge more for longer trade routes," explained Sand. "When measuring the tonnes-miles (TM) exports of US crude oil to Asia it is a longer route than Western Africa to Asia. That means they will be negatively impacted."
According to Bimco, Chinese traders have returned to purchasing U.S. crude oil in October but there is little visibility as to how much.