Different correlations are evaluated for the determination of ²⁴²Pu in Pu generated from PHWR reactors with an average burn-up of about 10,000MWd/TU. It is shown that the correlations involving ratios of Pu isotopes, except for ²⁴¹Pu, provide data with better confidence compared with those involving the atom% abundance. These correlations are also attractive when the decay period of the given sample is not known. In addition, it is shown that instead of using ²³⁹Pu atom% abundance alone (Swinhoe et al., 2010), either ²⁴⁰Pu atom% or a linear combination of ²³⁹Pu and ²⁴⁰Pu gives abundance of ²⁴²Pu with better reliability. The uncertainty due to different decay periods also remains unaffected when using the correlation involving both ²³⁹Pu and ²⁴⁰Pu atom%. The present conclusions are based on Pu isotopic composition data from PHWR reactors (²³⁹Pu 65-75%) whereas those reported by other investigators are for PWR and BWR types of reactors.