The reservoir, which cannot be found or identified directly by nowadays theory and technique, could be all called as subtle reservoir. It can be classified by discrimination difficulties, concealed modes, oil and gas accumulated dynamics mechanism, and it was put forward by the concealment of trap and difficulty of exploration discovery. So its meaning and content change with the development of exploration techniques as w ell as exploration theory. It should not be equaled to lithologic stratigraphic reservoir or nonstructural reservoir as some specific reservoirs would be ignored if only the two latter ones are regarded. Lithologic stratigraphic reservoirs are still the major exploration emphasis in subtle reservoirs which is a general expression of all the nonstructural trap sand includes some structural reservoirs that are difficult to find nowadays.The reservoir, which cannot be found or identified directly by nowadays theory and technique, could be all called as subtle reservoir. It can be classified by discrimination difficulties, concealed modes, oil and gas accumulated dynamics mechanism, and it was put forward by the concealment of trap and difficulty of exploration discovery. So its meaning and content change with the development of exploration techniques as w ell as exploration theory. It should not be equaled to lithologic stratigraphic reservoir or nonstructural reservoir as some specific reservoirs would be ignored if only the two latter ones are regarded. Lithologic stratigraphic reservoirs are still the major exploration emphasis in subtle reservoirs which is a general expression of all the nonstructural trap sand includes some structural reservoirs that are difficult to find nowadays.