In this paper, real crude oils are dealt with which are modeled with an average of 30 components. On the selected examples, neither the initial tie line, i.e., the tie line that extends through the original oil composition, nor the gas tie line, i.e., the tie line that extends through the injected gas composition, controls the miscibility process. In any case, the miscibility process is controlled by one of the (nc - 3) crossover tie lines, if nc is the number of components in the crude oil. However, it is shown that the miscibility process may be a pure vaporizing gas drive mechanism (VGDM). To be more precise, it is shown that a mixed condensing/vaporizing mechanism may, with increasing pressure, turn into a pure VGDM. This means that the classical definition of a VGDM, i.e., the lowest pressure at which the initial tie line is critical, must be changed. This is the main point of this paper. In the case of a VGDM controlled by a crossover tie line, the MMP (the lowest pressure at which the key crossover tie line becomes critical) may still be computed by a one cell simulation algorithm. Another aim of this paper is to explain what really happens during a one cell simulation and to give proof that such an algorithm may not make critical the initial or the gas tie line.