The objective of the present study is the evaluation of cv, the constant volume heat capacity along a locus of CJ states of nitromethane. Nitromethane (NM) was chosen because reliable measurements of its TCJare available, and there are requisite other data at varied initial densities &rgr;0. Acquisition of the latter is accomplished by changing the initial temperature, but this also changes the initial internal energy E0and creates some problems. An equation for cvwas developed which contains the experimental TCJ, assumed to be constant over the rather narrow range of &rgr;0of the other input data, and &ggr; =cP/cv, which still needs to be evaluated. Thus only provisional values of cvare presented. © 2004 American Institute of Physics