A high-profile North Sea discovery called for innovative engineering to enable representative formation fluid samples and critical measurements of H2S concentration. The wells operated by BG Group represented tough challenges on several fronts. The presence of a small concentration of sour gas was suspected, but its level was unknown. By using the Schlumberger Quicksilver Probe focused extraction of reservoir fluid, the time required to obtain an uncontaminated sample was reduced to 1/10th of the time. The reconfiguration of the test tool minimized H2S scavenging so accurate H2S concentrations could be quantified.