The thermal behavior, upon heating, was studied for four alkanes: eicosane. tetracosane, triacontane, and tetracontane at pressures from (10 to 150)MPa. Using a transitiometer. the calorimetric signal, pressure, and temperature were measured at a very slow heating rate to guarantee thermal equilibrium. It was found that from the compounds studied, eicosane was the only one that did not present a solid-solid transition; the other compounds show a solid-solid transition a few Kelvin below the solid-liquid transition temperature. This solid-solid transition disappears when the pressure is increased in a triple point of type: solid + solid + liquid. (C) 2008 Elsevier Ltd. All rights reserved.