II. Read and translate the text

As indicated above, both oil and gas reservoirs usually, start with a formation pressure that forces fluid into the well and sometimes to the surface. With artificial lift reservoir fluids may be produced as long as enough reservoir pressure remains to cause the fluids to flow into the well. Since a decline in reservoir pressure invariably accompanies fluid production, a point is reached at which commercial quantities of oil or gas no longer flow into the well. In natural gas reservoirs this does not usually occur until most of the gas is recovered. In nearly all crude-oil fields, however, less than one-third of the oil originally present can be produced using only the reservoir pressure.