Abstract: Micro-migration mechanism is currently the theoret-ical basis of non -seismic direct petroleum prospecting such as geochemical exploration.A thorough understand-ing of hydrocarbon phase state of petroleum micro-migra-tion is the precondition of further study of micro-migra-tion mechanism.Water phase containing oil and/or gas is the most common and preferentially functioning phase that leads to micro-migration of hydrocarbon.Hydrocarbon seepage also can occur in other phases under specific geologic conditions.