In order to study the effects of oxidation of sedimentary organic matter, low-temperature air oxidation experiments were conducted on a shale and its kerogen concentrate at 60 and 100 degrees C for 2-2048 h. The first stage of organic matter alteration was marked by a decrease in the extract yield, mainly attributed to evaporation and adsorption processes. During the second stage, the saturated and unsaturated biomarkers disappeared from the free hydrocarbons＇ phase and were probably incorporated into the polar phase through oxygen bonds. The third stage, characterized by the formation of short chain alkanes, was well correlated to the increase in the oxygen content of kerogen. The genesis of neoformed oxygen-bearing compounds including carboxylic acids was also observed.