International oil and gas investment disputes constitute an important part of investor-state dispute settlement (ISDS) system. Investment arbitration which is regarded as a prevalent dispute settlement mechanism in this area has come under severe criticism since it creates huge costs, lengthens the process, and devastates the parties’ long-term investment relationship. In recent years, the possibility of applying alternative dispute resolution (ADR) and hybrid dispute settlement mechanisms has largely been discussed. Mediation-arbitration (Med-Arb) is one of the hybrid integrated dispute settlement mechanisms which embodies flexibility, nonjudicial, and negotiate-oriented benefits of mediation and the finality advantage of arbitration simultaneously in a single process. In this method, mediation is first attempted by the parties before arbitration could be started; if settlement is not reached during the mediation phase, the appointed neutral or mediator will then act as (an) independent arbitrator(s), will continue the case under the arbitration process, and will render a binding arbitration award. In this method, if parties reach an agreement during the first phase (mediation process), they will not incur huge costs of lengthy investment arbitration. In this method, even if the first stage (mediation process) fails, since it has further clarified and narrowed down the disputes, then the arbitration process will be less lengthy and proceed more efficiently. Moreover, both investors and host states in oil and gas investment area do have strong ambitions to maintain the investment relationships. These goals are achieved better via adopting Med-Arb proceedings. The most noted concerns in this method relates to the issue of the impartiality of the neutral (mediator in the first stage) who acts as an arbitrator at the next stage. In other words, it may be argued that the confidential information learned by the neutral from the parties in the mediation stage may seriously impact on his/her impartiality in the arbitration stage. This issue can be responded in light of respecting party autonomy principle which selects the Med-Arb clearly and correctly for dispute settlement. This approach is affirmed and proposed by the UNCITRAL model law on international commercial conciliation (2002) as well. Also, concerns regarding the enforcement of international agreements resulting from mediation have already been addressed in the United Nations Convention on International Settlement Agreements Resulting from Mediation (Singapore Convention on Mediation), which has attained international acceptance by 51 state members so far.