Black-oil models neglect diffusive mechanisms such as molecular diffusion or mechanical dispersion; this omission produces a propensity to developing shocks. This paper aims to carry out an exhaustive identification of the kind of shocks that can occur when black-oil models are applied to problems in which the bubble-point varies and to establish the conditions under which they are generated. In addition to shocks of Buckley-Leverett type, two other classes of shocks and a bifurcation mechanism, are identified. Except for shocks of Buckley-Leverett type, all other shocks may occur in the presence of capillary forces. The paper contributes to clarify several aspects of black-oil models and to understand pathologies that occur in their numerical implementation.

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