Global warming has become one of the most popular topics on this planet in the past decades, since it is the challenge that needs the efforts from the whole mankind. Maritime transportation, which carries more than 90% of the global trade, plays a critical role in the contribution of green house gases (GHGs) emission. Unfortunately, the GHGs emitted by the global fleet still falls outside the emission reduction scheme established by the Kyoto Protocol. Alternative solutions are therefore strongly desired. Several marketbased measures are proposed and submitted to IMO for discussion and evaluation. In this paper, we choose to focus on one of these measures, namely Maritime Emissions Trading Scheme (METS). An optimization model integrating the classical fleet composition and deployment problem with the application of ETS (global or regional) is proposed. This model is used as a tool to study the actual impact of METS on fleet operation and corresponding CO 2 emission. The results of the computational study suggest that in the short term the implementation of METS may not guarantee further emission reduction in certain scenarios. However, in other scenarios with low bunker price, high allowance cost or global METS coverage, a more significant CO 2 decrease in the short term can be expected.Recently, the voice for implementing a market-based measure (MBM) in the shipping sector has become strong. An MBM addresses the negative externalities of a market, such as pollution, through market mechanisms. Different from command-and-control measures (e.g., legislations), a MBM offers economic incentives rather than fixed rules to achieve a more cost-effective and sustainable pollution control (Miola et al., 2011). In terms of shipping, an MBM can help to internalise the external costs of the fleet emission by making the ship owner or operator pay for the CO 2 emitted from their ships, which finally creates an incentive for them to cut the emissions (Psaraftis, 2012).Although seven MBM proposals have been submitted to the IMO for discussion and evaluation, it seems that only two of them, namely the Emissions Trading Scheme (ETS) and the GHG Fund, are favoured and widely studied in the literature (Shi, 2016). The ETS is a type of cap-and-trade system. In such a system, first a legally binding limit on total emissions (cap) during a certain period is set by the authority. Then the equivalent amount of emission allowances are issued by the administration and assigned to or purchased by different concerned parties. In the system, participants can choose to submit the allowance for their own emissions or trade with other players for cash based on the market price of the allowance. However, if all the issued allowances are consumed, no more emissions will be allowed due to the legal limit. Such a market-based cap-and-trade system will help achieve the emission reduction target with certainty as well as minimal costs. However, the uncertainty of the allowance price may cause problems, for example cost volatility and investment risks ...