The International Bar Association (IBA), Mediation Committee has recently published a draft version of rules for investor-state mediation. The scope of the Rules is as follows:
These rules are designed for the mediation of investment–related differences and disputes involving States and State entities, whether or not they arise out of an agreement. These rules apply when:
a) the mediating parties have agreed that these rules shall apply whether before or after the difference or dispute arises, or
b) the mediating parties have authorized the mediator or another person or institution to design a mediation process and that mediator, person or institution adopts these rules in whole or in part.
You may download the Rules (for free) here.