This invention provides a closed-loop system for in situ testing of formation fluid conditions and for selectively collecting substantially mud filtrate free formation fluid samples at original formation conditions. The system contains an elongated member having a probe that is sealingly placed against the wellbore formation to withdraw formation fluids. A surface controlled pump controls the flow of a fluid from the formation into a flowline placed in the elongated member. A pressure sensor provides downhole hydrostatic pressure and an acoustic density cell provides the speed of sound in the fluid, acoustic impedance of the fluid and acoustic absorption coefficient of the fluid in the flowline. The system determines the density and compressibility of the formation fluid in the flowline from the speed of sound in the fluid and acoustic impedance of the fluid. The formation of the bubbles are identified or detected from the acoustic absorption coefficient of the fluid in the flowline. The system controls the movement of fluid into the flowline to selectively collect the formation fluid samples that are substantially free from any mud filtrates while maintaining the fluid pressure above the bubble point pressure of the formation fluid. This invention provides a method for retrieving and collecting formation fluids from a zone of interest in a wellbore at the original formation conditions.