Metrics
Production decline is calculated in the form of barrels per day (or units of energy/time). A proper production decline curve would be drawn over the course of several years, judged on a logarithmic scale.
Exponential
A production decline curve might be considered aggressive if its production is exponentially negative. In other words, if the graph of the line of production approximates to -x^2 then the rate will quickly consolidate to zero. However, a more moderate production decline will be continuous. That means that each year it will decline in a similar percentage to the year before.
Peak Oil Theory
Peak oil theory was conceived by M. King Hubbert, who accurately predicted the peak and decline of Texas oil reserves in 1956. Today, this theory is being expanded to encompass the entire planet. Experts know that oil and gas will eventually be completely depleted. However, they argue over how much energy remains and what the production curve decline will look like. Some predict an aggressive exponential decline while other foresee a more modest continuous decline.
Hydraulic Fracking
Energy companies have attempted to avoid exponential decline in production through technology and more advanced exploration techniques. First among these is the concept of "hydraulic fracking." This technique creates additional potential energy by shooting bursts of water and air to break up rocks that contain oil and gas. The Marcellus Shale, which runs through Tennessee up to Pennsylvania and New York, among other places. has up to 490 trillion cubic feet of gas that are now becoming available as fracking comes into wider use.