The Quartet-HT high-performance downhole reservoir testing system from Schlumberger combines four downhole technologies into one advanced downhole string design for ultra-high-temperature reservoirs up to 210 degC (410 degF). The Quartet-HT system offers multiple advantages over conventional drillstem test configurations including shorter string design, lower operating pressure, less nitrogen, fewer seals and connections, multicycle flexibility, single-trip efficiency, all-ceramic multichip module design, and high-resolution quartz measurements. With the rugged test string, operators can isolate the zone, control the flow, measure pressure and temperature, and acquire and retrieve multiple reservoir-representative fluid samples in a single run at ultrahigh temperatures.