Population Dynamics P systems provide a formal framework for ecological modelling having a probabilistic (while keeping the maximal parallelism). Several simulation algorithms have been developed always trying to reach higher reliability in the way they reproduce the behaviour of the ecosystems being modelled. It is natural for those algorithms to classify the rules into blocks, comprising rules that share identical left-hand side. Previous algorithms, such as the Binomial Block Based (BBB) or the Direct Non Deterministic distribution with Probabilities (DNDP), do not define a deterministic behaviour for blocks of rules competing for the same resources. In this paper we introduce the Direct distribution based on Consistent Blocks Algorithm (DCBA), a simulation algorithm which addresses that inherent non-determinism of the model by distributing proportionally the resources.