The main objective of the present work of thesis was: determining the relations between the variables physicalthermo (density, specific heat and thermal conductivity), with pressure and the temperature of liquefied petroleum gas. The present investigation has quantitative focus with level of deepening with level of deepening predictive and I design correlational. The modeling of multiple regression has come true, which has allowed determining the relations between the variables termofísicas with pressure and temperature. The type of sampling was the probabilistic no, coming true for each variable termofísica a total of 101 simulations; therefore, as three variables are physicalthermo, the total sample had a size of 303. The results that they got from the relations between the variables physicalthermo, with pressure and temperature are: for density: ???=562.33?1.28??+0.04??, ??2=0.9986;...