AbstractIn the BAT ground water sampling system, a stainless steel probe with a porous filter element is pushed vertically to the desired sampling depth. An evacuated glass sampling tube is then lowered down the penetration rods where it makes contact with the filter via a hypodermic needle and draws a pore fluid sample.An investigation of the system was carried out at a number of sites contaminated by leaking underground gasoline storage tanks. Ground water samples obtained using the BAT system and adjacent monitoring wells were analyzed for volatile organic compounds (VOCs).Because the BAT system is an in situ penetration device with a small filter length, it is possible to determine variations in contaminant concentration with depth. BAT samples in general exhibited higher recovery of VOCs than did bailer samples from adjacent monitoring wells screened over large intervals.Much higher levels of VOCs were recovered when the probe was used with its 316 stainless steel filter than when using the high‐density polyethylene (HDPE) filter. Significant sorption apparently occurred on the latter filter.Because the BAT sample tubes are sealed and remain a closed system, the in situ water pressure is maintained. No significant loss of VOCs was found in sampling tubes containing headspace. Samples from the upper tube in the cascaded setup with headspace recovered levels of VOCs as high, or in a few cases higher, than the lower, no‐headspace tu