The Cumulative Prospect Theory, as it was specified by Tversky and Kahneman (1992) does not explain the St Petersburg Paradox. This study shows that the solutions proposed in the literature (Blavatskky, 2005; Rieger and Wang, 2006) to guarantee, under rank dependant models, finite subjective utilities for any prospects with finite expected values have to cope with many limitations. In that framework, CPT fails to accommodate both gambling and insurance behavior. We suggested to replace the weighting function generally proposed in the literature with another specification which respects the following properties. 1) In order to guarantee finite subjective values for all prospects with finite expected values, the slope at zero should be finite. 2) To account for the fourfold pattern of risk attitudes, the probability weighting should be strong enough to overcome the concavity of the value function.