Option pricing, decision trees and Monte Carlo simulations are First Step - NPV for the base case three methods used for evaluating projects. In this paper their The first step in evaluating any project is to set up a base case similarities and differences are compared from three points scenario and to calculate its NPV using the parameter values of view:- how they handle uncertainty in the values of key that have been agreed upon. This assumes that the values of parameters such as the reserves, the oil price and costs; how the input parameters are known: they incorporate the time value of money and whether they allow for managerial flexibility. We show that despite their original oil in place, obvious differences, they are in fact different facets of a general decline rate, project evaluation framework which has the static base case oil prices for each year, scenario as its simplest form. Compromises have to be made costs for each year, when modelling the complexity of the real world. These three discount rate, approaches can be obtained from the general framework by tax structure, etc. focussing on certainty aspects.