As part of the Megamaser Cosmology Project ( MCP ) , we present VLBI maps of nuclear water masers toward five galaxies . The masers originate in sub-parsec circumnuclear disks . For three of the galaxies , we fit Keplerian rotation curves to estimate their supermassive black hole ( SMBH ) masses , and determine ( 2.9 \pm 0.3 ) \times~ { } 10 ^ { 6 } M _ { \odot } for J0437+2456 , ( 1.7 \pm 0.1 ) \times~ { } 10 ^ { 7 } M _ { \odot } for ESO 558 - G009 , and ( 1.1 \pm 0.2 ) \times~ { } 10 ^ { 7 } M _ { \odot } for NGC 5495 . In the other two galaxies , Mrk 1029 and NGC 1320 , the geometry and dynamics are more complicated and preclude robust black hole mass estimates . Including our new results , we compiled a list of 15 VLBI-confirmed disk maser galaxies with robust SMBH mass measurements . With this sample , we confirm the empirical relation of R _ { out } \propto 0.3 M _ { SMBH } reported in Wardle & Yusef-Zadeh ( 2012 ) . We also find a tentative correlation between maser disk outer radii and WISE luminosity . We find no correlations of maser disk size with X-ray 2-10 keV luminosity or [ O III ] luminosity .