The Oil Drum

Some inputs are "free", light from the sun, coal in the ground etc. you have to count exploration/manufacturing costs all the way to energy consumer.  It can never be infinite and if it is less than 1 it is not worth doing. Arguably if it is near 1 its not worth doing.

;-), it's a question of boundries.  It's true that the universe has an EROEI of 1 ... but a lion or human operates on a smaller scale.

You are right, slaphappy, the efficiency of an energy transformation can never be greater than one. The laws of thermodynamics tell us this. Typically, however, we refer to this as efficiency, not net energy. Allow me to elaborate.

1st Law of Thermodynamics:
Energy cannot be consumed or destroyed--only transformed from one form to another. (Energy must be conserved.)

2nd Law of Thermodynamics:
When energy is transformed from one form to another, some of the energy is necessarily transformed into heat. (Entropy always increases).

In a closed system--a system in which no energy can enter or leave--every energy transformation increases entropy and makes less transformable energy available in the system. The earth, however, is an open system--there is a constant flow of energy arriving at earth from somewhere else and a constant flow of energy escaping from the earth.

The fundamental energy source for all life on earth is the sun. Plants (and some bacteria) transform electromagnetic energy (light) into chemical energy. Much of the light energy is lost to heat during this transformation. Living things then  transform that energy into other forms to carry out life processes (e.g. organisms move by transforming chemical energy into kinetic energy). If the organism has stored chemical energy and dies before it can be used, that energy can be "harvested" by other organisms. Thus they have found an energy reservoir.

We can sum up the process of energy transformation on earth:
--> indicates an energy transformation

1. mass enegery --> heat energy (via thermonuclear fusion in the core of the sun)
   
2. heat energy --> electromagnetic energy (via radiation at the sun's surface)
   
3. electromagnetic energy --> chemical energy (via photosynthesis by organisms on earth)
   

Energy stored in chemical form can be transformed by humans to do "useful work". Here are some common exosomatic energy transformations that humans initiate (i.e. energy transformed outside our bodies, not used internally):

4. chemical energy --> heat energy (via oxidation/combustion)
   
5. heat energy --> kinetic energy (via heat engines, e.g. steam or ICE)
   
6. kinetic energy --> electromagnetic energy (via electric generators)
   
7. electromagnetic energy --> heat energy (via your stove, TV, computer, etc.)

In transportation, Step 5 is the human end-use--kinetic energy is the form of energy we desire in order to quickly transport ourselves in cars, airplanes, etc.

The conclusion of Step 6 provides energy in the form of electricity.

In every single step described above, energy is lost as heat during the transformation process.

A oil deposit is a reservoir of energy, that is, it is a large reserve of stored chemical energy. All of that stored energy can be obtained and released (transformed) by using a much smaller amount of energy. This is EROEI.