Arbitral awards are immune to errors of fact and law, as the Hon. Ian Binnie C.C., Q.C. so eloquently noted at the 13th Annual ITA-ASIL Conference. Still, even if we consider that substantively erroneous awards may be enforceable or not subject to substantive review, is it not in the arbitrators’ inherent duty to resolve the dispute in an efficient manner, providing adequate reasoning based on facts and/or law? From where does this ethical duty stem, and why does it matter if the dispute arises from a treaty-based investment arbitration? This paper will attempt to answer these questions, identifying the new trends on ethics regulations of arbitrators, as reflected in applicable international instruments. In particular, this paper will focus on the developments addressed by recent International Investment Agreements (IIAs), such as the Trans-Pacific Partnership (TPP) and the Comprehensive Economic and Trade Agreement (CETA).