2 to settling vessel 3 virtually no gas separation occurs as the fluid flows from annulus 31 between separator 8 and casing 9 into settling vessel 3 the horizontal component of the movement perpendicular to the gravitational field causes one part of the separation the other part takes place within annulus 33 between the inner side surface of settling vessel 3 and production tubing 22 where flow of the cascade type occurs the gas separated rises through the annulus in the well 25 to the surface passing through control valve 29 the liquid rises through suction tubing 6 passes through pump 12 and reaches the surface via production column 22 openings 2 in the upper side surface part of settling vessel 3 have diameters and a distribution such that the flow of fluids per unit length of the perforated vessel is made small the intention is not to carry the gas which is within annulus 31 between separator 8 and well casing 9 into vessel 3 and in particular not to cause flooding of liquid within annulus 33 between the inner side surface of settling vessel 3 and production column 22 where the initial descending velocity of the liquid is low on the other hand the diameter of openings 2 should be large enough so as not to cause clogging by sand or detritus as the quantity of accumulated liquid increases settling vessel 3 moves downwards through the action of the weight of the liquid which is greater than the sum of the thrust received from the liquid outside settling vessel 3 and the action of spring.