Homeowners, businesses and utilities across much of the United States were keeping a close watch on fuel supplies Wednesday as a record-setting cold snap caused demand for heating oil and natural gas to soar.

With heating units in homes and commercial buildings running furiously to fend off the deep freeze, power companies warned of possible fuel shortages to come. Many utilities turned to coal and oil to generate electricity as the price of natural gas, their usual fuel of choice, surged.

“The sustained cold is requiring round-the-clock usage of some of these oil-fired generators, and some are already running short on fuel,” said Marcia Blomberg, a spokeswoman for ISO New England, which operates a regional grid and wholesale power markets.