Due to dwindling natural resources and continually increasing energy demands, renewable energy may be the solution to the world’s future energy needs. The oceans represent a large reservoir of energy and marine derived renewable energy may in turn represent a significant source of global electricity. In particular, the marine renewables reviewed in this study are ocean thermal energy conversion and wave energy. Unlike more mainstream renewables, little research has been undertaken to determine the capabilities of these technologies. However, the authors believe that these technologies have the potential to contribute significantly to the global energy market. Global potential maps for each technology were constructed using analysis of data sets provided by the International Research Institute for Climate and Society (Columbia University) and a Geographic Information System. These show the best viability of OTEC to be concentrated around the Equator, where the vertical ocean temperature gradients are at least 20°C/km, and that the most suitable areas for wave power are concentrated between the latitudes of roughly 40 to 60° N and S, where surface wind speeds average at least 8 m/s. Given these areas, gross potential outputs were calculated to be 605 TW for OTEC and 3368 TW for wave power, 1% of which is still greater than the global electricity demand (13.2 PWh, or 1.51 TW of power, in 2000 (EIA, 2007)). These results are promising, but they do not reflect technological, sociological and economical limitations. The environmental impacts of these technologies may range from local effects on ecosystems and biodiversity to long-term global climate and oceanic implications. Compared to modern non-renewable energy sources, these technologies have no significant greenhouse gas emissions. Given the globally significant potential outputs and limited environmental impacts of OTEC and wave energy, it is clear that marine renewable energy technologies are viable as future sources of electricity.