Abstract: A method and apparatus for determining both the thermal conductivity, k, and specific heat, c.sub.p, of a fluid of interest are disclosed. An embodiment uses proximately positioned resistive heater and thermal sensor coupled by the fluid of interest. A pulse of electrical energy is applied to the heater of a level and duration such that both a transient change and a substantially steady-state temperature occur in the sensor. The k of the fluid of interest is determined based upon a known relation between the sensor output and k at steady-state sensor temperature; and c.sub.p of the fluid of interest is determined based on a known relation among k, the rate of change of the sensor output during a transient temperature change in the sensor and c.sub.p.