The rise of global uncertainty and oil productivity rocked the energy commodity market last year, causing significant fluctuation in the energy commodity price in 2018, U.S. Energy Information Administration (EIA) said on Wednesday.

The S&P Goldman Sachs Commodity Index (GSCI), a weighted average of the price index that reflects multiple types of commodities, showed that energy price fluctuated through the year, said EIA.

"For most of 2018, crude oil prices rose because of the increased potential for supply constraints and declining global petroleum inventories," said EIA.

Brent crude oil, a major trading classification which serves as a benchmark price, once reached a four-year high of 86 dollars per barrel on Oct. 3, 2018.

However, compared to the beginning of the year, the GSCI energy index dropped 21 percent at the end of 2018, after a nearly 25 percent gain in the first three quarters, according to EIA.

Since the energy index tends to follow major price movements in the crude oil market, uncertainties over the crude oil production contributed to the rise or drop in the index, said EIA.

"When the United States announced its intention to reinstitute sanctions against Iran, several major oil importing countries began decreasing the amount of Iranian crude oil they imported," EIA said.

Meanwhile, waivers granted to some importers of Iranian crude oil eased concerns about crude oil availability, said EIA.

Crude oil production in the United States, Russia and Saudi Arabia was at or near record highs, also easing the potential for supply constraints and declining inventories.

Looking into the next year, a slowed economy could further bring down the oil demand. Last month, U.S. Federal Reserve lowered its 2019 growth forecast for U.S. economy from 2.5 percent to 2.3 percent.

"Concerns about slowing global economic growth and its impact on oil demand also contributed to recent declines in crude oil prices," EIA said.