HOUSTON — The world’s oil producers and their customers entered a new period of uncertainty on Monday as renewed American economic sanctions against Iran took effect.

Having withdrawn from the seven-nation deal negotiated under his predecessor to curb Iranian nuclear efforts, President Trump is aiming to pressure Iran to curb its political and military activities across the Middle East. And the administration is betting that its policy will inflict pain on Tehran without causing a spike in oil prices or an aggressive reaction.

It is a gamble that could eventually cost American consumers at the gasoline pump. But the initial impact has been relatively benign. Oil prices have been declining in recent weeks, even with sanctions on the horizon.

What do the sanctions do?

The sanctions take aim not only at Iranian oil exports, but also at international shipping companies, banks, insurers and port operators doing business with Iran. United States trade with Iran is already tightly controlled, but the administration is threatening to exclude international companies from the American financial system if they trade, finance or otherwise serve the interest of Iranian oil exports.