Drilling in the Qiongdongnan basin offshore China often has resulted in failure to reach desired objectives. Bottomhole temperatures as high as 475 degreesF and pressures requiring mud weights as great as 19.5 1bm/gal severely limit drilling fluid performance and often contribute to failure to achieve desired drilling objectives. Well Yacheng 21-1-4 was drilled in this basin with a semisubmersible rig. After total depth (TD) was reached, logs were run to bottom without incident with no significant drilling fluid related problems. This success is attributed to innovative, fit-for-purpose drilling fluids, and rigorous prewell planning over a 2-year period before drilling began. The full-length paper describes the holistic approach to drilling-fluid engineering for extreme well conditions.