Offshore wind and wave power are renewable energy sources that share the marine environment. Collocating these systems can reduce power variability; however, the extent of this differs between sites. Regional differences in combined system variability are investigated. Potential power output of wind and wave systems is simulated for sites throughout the US East and West Coasts and UK North Sea using field observations of met-ocean conditions. The power production potential is approximated using an idealized power curve of the Siemens Gamesa SWT-6.0-154 6 MW wind turbine and the Pelamis 750 kW wave energy converter power matrix. The regional comparative approach provides novel insight into collocated system power variability on the US East Coast, and how it contrasts with the previously studied US West Coast and UK North Sea. Hourly and diurnal variability are found to decrease on the US West Coast and UK North Sea, with minimal effect on the US East Coast. The benefits for the West Coast extend to seasonal time scales (but as expected not to annual scales), but benefits for all regions depend on the specific wind-wave capacity mix. Reduced variability can benefit collocated wind and wave power, but these effects differ regionally and must be assessed locally.