A vial adapter for a closed fluid transfer system, the vial adapter including a base defining an opening having a plurality of retainers extending around the opening of the base and being configured to snap-fit connect to a neck ("N") of a vial ("V"), characterized in that the base defines a lower inner annular rim and an outer annular rim and a cavity therebetween, the vial adapter further including: a cover supported on the outer rim of the base, wherein an expansion chamber is defined within the cover and the base; an adapter support situated within the cavity of the base, the adapter support including: an annular flange for seating on the lower inner annular rim of the base and forming a fluid tight seal therebetween; an annular wall extending from the annular flange and defining an upper inner annular rim, wherein the cover is also supported on the upper inner annular rim; a male stem extending in a first direction from the annular flange, the male stem for selective connection to and insertion into an open distal end of a syringe adapter, the male stem defining a lumen extending therethrough; a pair of opposed guide pins (53, 55) extending radially outward from the male stem; a pair of opposed guide surfaces (57, 59) extending radially outward from the male stem at a location proximal of the guide pins (53, 55) and being in registration with the guide pins (53, 55); and a seal extending across the lumen of the male stem; and a spike extending in a second direction from the annular flange, wherein the spike extends into the opening of the base, wherein the spike includes a first lumen being in fluid communication with the lumen of the male stem, and wherein the spike includes a second lumen being in fluid communication with the expansion chamber; and a bladder extending between the inner upper annular rim and the outer annular rim of the base. a cover supported on the outer rim of the base, wherein an expansion chamber is defined within the cover and the base; an adapter support situated within the cavity of the base, the adapter support including: an annular flange for seating on the lower inner annular rim of the base and forming a fluid tight seal therebetween; an annular wall extending from the annular flange and defining an upper inner annular rim, wherein the cover is also supported on the upper inner annular rim; a male stem extending in a first direction from the annular flange, the male stem for selective connection to and insertion into an open distal end of a syringe adapter, the male stem defining a lumen extending therethrough; a pair of opposed guide pins (53, 55) extending radially outward from the male stem; a pair of opposed guide surfaces (57, 59) extending radially outward from the male stem at a location proximal of the guide pins (53, 55) and being in registration with the guide pins (53, 55); and a seal extending across the lumen of the male stem; and an annular flange for seating on the lower inner annular rim of the base and forming a fluid tight seal therebetween; an annular wall extending from the annular flange and defining an upper inner annular rim, wherein the cover is also supported on the upper inner annular rim; a male stem extending in a first direction from the annular flange, the male stem for selective connection to and insertion into an open distal end of a syringe adapter, the male stem defining a lumen extending therethrough; a pair of opposed guide pins (53, 55) extending radially outward from the male stem; a pair of opposed guide surfaces (57, 59) extending radially outward from the male stem at a location proximal of the guide pins (53, 55) and being in registration with the guide pins (53, 55); and a seal extending across the lumen of the male stem; and