Phase behavior of methane pentane mixture and anomalies of the isochoric heat capacity C-rho,C-x and the derivative (partial derivative P/partial derivative T)(rho,x) have been studied experimentally in the vicinity of liquid vapor critical point at three pentane concentrations, namely, for 0.0196, 0.0345, and 0.096 mol fraction of pentane. It has been shown that for two low pentane concentrations the behavior of the heat capacity C-rho,C-x and (partial derivative P/partial derivative T)(rho,x) differs substantially from both theoretically predicted and experimentally observed behavior of the properties in other mixtures. We suggest that the reason of such unusual behavior is caused by the proximity of the mixture critical locus to the tricritical point at low pentane concentrations. On the other hand dew -bubble curves (DBC) of the methane-pentane mixtures for all studied concentrations do not exhibit any special features and thus can be described theoretically within the scope of the conventional scaling approach. (C) 2015 Published by Elsevier B.V.