International commercial gas sale agreements are often characterised by a duration of twenty years or more. Consequently, when unforeseen events alter market conditions the contractual equilibrium originally found by the parties is disrupted, giving rise to the necessity to renegotiate and adapt the agreement. If negotiation fails, the parties in most cases submit the matter to arbitration. This comprehensive analysis of what can happen under such circumstances proceeds from an in-depth consideration of the power of arbitrators to intervene on the agreement in the light of arbitrability and procedural law. The author fully explains the complex special nature of gas pricing and contract clauses, and takes into account such features as the following, especially in the wake of the 2009 crisis as it affected the gas sector: - take or pay clauses; - mechanisms for gas price calculation; - price review and price re-opener clauses; - hardship provisions; - problems arising from the absence of a specific clause providing for adaptation/adjustment; - effect on contracts of the emergence and development of spot or traded gas markets; and - trend toward introducing spot-market elements into an oil-indexed price formula. The analysis draws on interviews with lawyers and arbitrators who have been involved in recent proceedings regarding gas sale contract adaptations, and also considers court decisions issued in setting aside or enforcing arbitration awards handed down in energy disputes. A central discussion throughout this book is the possible responses to the question of whether it is possible to determine a principle of law justifying the arbitrator’s power to intervene in contract adaptation. All professionals involved in the production, wholesaling, or distribution of gas will find this book indispensable. It will also be of special value to practitioners, policymakers, and regulators in the fields of energy law and environmental law.