Many industries are state or federally regulated. Companies in those industries must disclose information about themselves to those agencies.
In addition to disclosing financial information not necessarily found elsewhere, the information is often expressed using specific industry terminology and measurements.
Some agencies do not disclose the actual information or reports over the Internet and these reports must be requested.
Key agencies are the Federal Energy Regulatory Commission (FERC) and the Department of Energy (DOE). Note that some FERC reports aren't online and must be requested.