There are two approaches for evaluating two or more investment projects. One is a total investment approach and the other is an incremental investment approach. We present that ranking projects by the latter is not sufficient for an investor to accept the next best alternative. We prove that ranking projects by the former is superior to that by the latter. We also prove that the ranks obtained by the criteria like ORR and B/C ratio are consistent to the ranks by DCF criteria. However the result is different when IRR is adapted