Estimating hydrocarbon resources and reserves may be divided into three phases:

1. future potential or undiscovered resources on an exploration play, basin or province scale;

2. undiscovered resources on a prospect scale; and

3. discovered reserves.

The basic parameters to be assessed are much the same in all three phases – expected productive area, pay thickness and recovery factors or hydrocarbon bearing reservoir volume and fluid saturations. The availability and accuracy of data required for parameter assessment tend to increase from the first through the third phase. In the first phase and in many cases in the second, the input data may be estimated within ranges as on a probability scale because they cannot be measured. After discovery, in the development phase, the parameters are generally known more accurately and input may be actual remote or direct measurements used as single values to develop more accurate estimates of hydrocarbon volumes than in the undiscovered resource phases.

The petroleum industry requires a complex array of data to explore for and develop hydrocarbon accumulations ranging from simple compilations of directly measured values to complex sets of seismic, remote sensing, electronic, radioactive, acoustic and other indirect measurements of physical properties. All data needed for estimating volumes of hydrocarbons are collected in the normal course of exploration and exploitation.

The great quantities of data required for detection, location and appraisal of petroleum resources together with the sophisticated, detailed processing required to render usable interpretations have promoted the extensive and intensive use of computer processing in all phases of resource and reserve estimates.