Abstract Speed is often touted as an advantage of arbitration. In recent years, however, some have worried that investment arbitration risks losing this advantage. Concerns about the length of investor-State dispute settlement (ISDS) proceedings have also been raised in the discussion about ISDS reform. This article analyses the duration of ISDS proceedings applying a data-centric approach and evaluates the impact of proposed ISDS reforms on the duration of proceedings. After some terminological clarifications on when proceedings are ‘excessively’ long, the article sets out the evidence on the length of proceedings using several data-sets. As a comparator, we present data on the length of World Trade Organization (WTO) proceedings, even though we urge caution as to the usefulness of such a comparator. The article then discusses the impact of various reform proposals on the duration of proceedings, namely improving ISDS, adding an appellate mechanism, establishing a multilateral investment court and abolishing ISDS.