The Securities and Exchange Commission on Thursday proposed updated rules for energy companies that will require them to provide more detailed information to investors when reporting their oil and gas reserves.

Reserves are an oil company's most valuable asset and a critical indicator of its long-term financial prospects. Any reduction in their estimated size is a concern for investors. The SEC's current reporting rules for oil and natural gas reserves were adopted more than 25 years ago, and the proposed changes are intended to reflect technological changes in how oil companies determine their proven reserves.