A technique is presented that has been successfully demonstrated to non-intrusively and quickly sample gases typically found in PCV systems. Color Detection Tubes (CDTs) were used with a simple sampling arrangement to monitor CO{sub 2}, NO{sub x}, O{sub 2}, and H{sub 2}O(g) at the closure line, crankcase, and PCV line. Measurements were accurate and could be made instantaneously. Short Path Thermal Desorbtion Tubes (SPTDTs) were used at the same engine locations for the characterization of fuel- and oil-derived hydrocarbon (HC) fractions and required only 50 cc samples. High engine loads caused pushover of blowby vapors as indicated by increased concentrations of CO{sub 2}, NO{sub x}, H{sub 2}O(g), and fuel HCs in the engines` fresh air inlets during WOT operation. Peak concentrations of blowby vapors were measured in the crankcase under no load and part throttle conditions. Oxygen concentrations always opposed the trends of CO{sub 2}, NO{sub x}, and H{sub 2}O(g). SPTDT data revealed that the PCV system consumes approximately 100-200 times more fuel vapors than oil vapors, on a mass basis; however, PCV-derived oil consumption represented almost 12 percent of total engine oil consumption under no load conditions. 8 refs., 17 figs.