US energy statistics: electricity, petroleum, gas.
EIA Open Data API is a free Environment API that requires apiKey authentication, is served over HTTPS and has unconfirmed CORS support.
Energy Information Administration - EIA - Official Energy Statistics from the U.S. Government
Details from eia.gov.

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The EIA Open Data API is provided by U.S. Energy Information Administration (EIA) (eia.gov). Energy Information Administration - EIA - Official Energy Statistics from the U.S. Government
Yes. The EIA Open Data API is listed in the Environment category of the public-apis directory, which only includes APIs that are free or have a free tier. Check its documentation for rate limits and paid plans.
Yes. The EIA Open Data API uses apiKey authentication, so you need to register for credentials before making requests.
CORS support for the EIA Open Data API is unknown. Test a request from the browser, and fall back to a server-side call if it is blocked.
Yes. The EIA Open Data API is served over HTTPS, so it's safe to use in production.