This study aims to quantify and analyse emissions from marine vessels that are capable of operating on liquefied natural gas (LNG) but continue to rely on conventional fuels, largely due to the limited availability of LNG bunkering stations (BSs) over long distances. Four regions were identified as having high concentrations of LNG-fueled vessels but limited access to operational BSs: the West Coast of the United States of America (USA), South Africa-Good Hope-Madagascar, Northwest Africa, and Brazil. This selection is based on the geographical distribution of these ships and existing infrastructure conditions. Hourly greenhouse gas (GHG) emissions were estimated by considering the power outputs of the main and auxiliary engines, specific fuel consumption (SFC) rates, and the emission factors for the vessels' liquid and gas operating modes. Container ships exhibit the highest hourly GHG emissions among vessel types, reaching 31.49 t/h in liquid mode and 23.68 t/h in gas mode. This is followed by crude oil tankers (6.3-14.01 t/h in liquid mode), bulk carriers (8.06 t/h in liquid and 6.06 t/h in gas), and car carriers (6.3-7.66 t/h in liquid mode). Gas mode provides a 19-29 % reduction in emissions across these vessel categories. In high-traffic regions such as the West Coast of the USA and South Africa-Good Hope-Madagascar, annual GHG emissions from LNG-fueled ships total 1.84 Mt and 2.19 Mt in liquid mode, respectively. Full adoption of gas mode could yield potential 24-26 % reductions, thereby contributing substantially to the mitigation of global maritime GHG emissions.