The solubilities of p-t-butylcalix[n]arenes (n = 4,6,8) and calix[4]arene have been measured in supercritical carbon dioxide. Solubility measurements were conducted in a high pressure cell with in situ spectrophotometric detection. Measurements were taken over the ranges of 10 to 20 MPa and 40 to 60 degrees C. The p-t-butylcalix[il]arene showed solubility approximately 10 fold higher than both p-t-butylcalix[6]arene and p-t-butylcalix[8]arene with a maximum measured solubility over the studied pressure and temperature ranges of 1.84 x 10(-5) mol/l. A comparison of these results with measurements made with a commercially available analytical SFE unit for p-t-butylcalix[4]arene showed less than 10% deviation between the two sets of data over a common range of conditions. The SFE unit allows measurements to be made over significantly wider ranges of pressure and temperature than are currently available using the solubility cell. Published by Elsevier Science B.V.