Oil prices rose 1% on Tuesday amid concerns about global supply constraints caused by the Libyan civil war, declining exports from Venezuela and Iran, but uncertainty about OPEC-led production cuts has limited oil price increases.

Brent crude oil futures closed up $0.54, or 0.76%, at $71.72 a barrel. U.S. crude oil futures rose $0.65, or 1%, to close at $64.05 a barrel.

In Libya, fighting between the Haftar-led Libyan National Army and the internationally recognized government has increased the likelihood of a decline in the country’s supply. Libya is a member of OPEC.

U.S. sanctions against Iran and Venezuela, the other two OPEC members, have led to a reduction in oil exports. According to tanker data and industry sources, Iran’s crude oil exports in April have fallen to the lowest level since then.

“Global supply is falling faster than people think. The imbalance between supply and demand in the market, “said Phil Flynn, an analyst at Price Futures Group.” The continued decline in Venezuela’s oil supply will have an impact, and OPEC production cuts will also play a role.

However, downward pressure has increased on Russia’s willingness to stick to OPEC-led production cuts and expectations of increased inventories in the United States.

Oil prices have risen by more than 30% this year, driven by agreements between OPEC and other oil producers, including Russia. The organization has been cutting production since January 1 and will decide in June whether to continue cutting production.

An official from Russian natural gas giant Gazprom said Tuesday that the global oil agreement signed by OPEC and its allies is expected to end in the first half of this year.

U.S. crude oil stocks are expected to increase by 1.7 million barrels last week, the fourth consecutive week of increase, also putting pressure on oil prices. Nevertheless, gasoline stocks have declined for nine consecutive weeks, with refining rates of less than 90% of total capacity since early February due to seasonal maintenance.