Abstract: A method of simultaneously measuring thermal conductivity and heat capacity of a fluid, using a heat conduction calorimeter having a reference fluid in a first cell and a sample fluid in a second cell includes the steps of calibrating the calorimeter using a standard fluid having known thermal conductivity and heat capacity over a range of temperatures and the reference fluid to determine a set of sensitivity parameters, {a.sub.n.sup.ij }, of the calorimeter, wherein the a.sub.n.sup.ij are functions of the calorimeter, temperature and the reference fluid; applying a square wave heat pulse to the calorimeter containing said sample fluid and said reference fluid; measuring the thermal response curve to the square wave heat pulse, wherein the thermal response curve is a function of time, temperature of the measurement, thermal properties of the sample fluid, and thermal properties of the reference fluid; reducing the response curve to a set of discrete characteristic parameters, {p.sub.