The solubilities of 3,9-dichloro-2,4,8,10-tetraoxa-3,9-diphosphaspiro[5.5]undecane-3,9-dioxide from (303.15 to 311.35) K in dichloromethane and from (298.15 to 357.65) K in acetic acid, 3,9-dihydroxy-2,4,8,10-tetraoxa-3,9- diphosphaspiro[5.5]undecane-3,9-dioxide from (309.35 to 331.55) K in acetonitrile and from (295.75 to 319.15) K in acetone, 2,4,8,10-tetraoxa-3,9-dioxide-3,9-diphosphaspiro[5.5] undecane-3,9-melamine salt from (293.15 to 343.15) K in water, and 3,9-(bis-2,2'-carboxyetheyl)-3,9-dioxo-2,4,8,10-tetraoxa-3,9-diphosphaspiro[5.5] undecane from (332.15 to 342.15) K in ethyl acetate were determined using a gravimetric method. The estimated uncertainty of all the solubility values based on error analysis and repeated observations was within 2.5 %.