BISMARCK, N.D. — Donald J. Trump traveled Thursday to the heart of America’s oil and gas boom, where he called for more fossil fuel drilling and fewer environmental regulations while vowing to “cancel the Paris climate agreement,” the 2015 accord committing nearly every nation to taking action to curb climate change.

Laying out his positions on energy and the environment at an oil industry conference in North Dakota, he vowed to rescind President Obama’s signature climate change rules and revive construction of the Keystone XL pipeline, which would bring petroleum from Canada’s oil sands to Gulf Coast refineries.

It was the latest in a series of recent policy addresses, including on Israel and foreign policy, intended to position Mr. Trump, the real estate mogul and reality show star, as credible on substantive issues now that he is the presumptive Republican presidential nominee.

But experts remain skeptical of Mr. Trump’s command of the complexities of the global energy economy. And he made claims, such as a promise to restore jobs lost in coal mining, that essentially defy free-market forces.