Investigating the Share of Civil Liability of Multiple Tort feasors in Iranian Law and the Principles of European Tort Law

In an event that more than one factor is involved in the occurrence of a loss to another, after having obtained that two or more factors caused a loss to another, each of them will be responsible for the compensation of the victim. But how is the share of responsibility for each factor determined and on what basis can each share be determined and the amount of damage distributed? Three criteria have been raised in this regard, distribution of responsibility in equality, distribution of responsibility by the extent of influence and distribution of responsibility by the degree of culpability. In this paper, by describing the various assumptions of multiple tortfeasors,  each of these criteria has been investigated according to the arguments and legal principles and objectives of civil liability, and it has been proved that the primary principle is the distribution of responsibility to the extent of influence, and with the lack of evidence and proof for the difference in influence or equivalence of the actions of the responsible actors in causing loss, the distribution of responsibility in equality is applied.