What is energy return on energy invested (EROEI) and why is it important for assessing energy resources?

• A. EROEI equals energy invested divided by energy returned.
• B. EROEI equals energy returned divided by energy invested to obtain and deliver the energy; higher is better.
• C. EROEI measures environmental impact per unit energy.
• D. EROEI is the price of energy production.

Answer: (B)

EROEI measures how much energy you get back from a resource compared to how much energy you had to put in to obtain and deliver that energy. It’s calculated as energy returned divided by energy invested, and a higher ratio means you net more energy from the resource. This matters because it tells you how energetically efficient a resource is: easier-to-extract resources tend to have high EROEI, while harder-to-recover ones (like oil sands or shale) have lower EROEI due to more energy used in extraction and processing. If EROEI is low, close to 1, most of the produced energy is consumed just to gather and refine it, leaving little net energy. The other options describe different ideas (an inverse ratio, environmental impact per unit energy, or price) and don’t capture the energy-accounting meaning of EROEI.