1. n. 
A neutral to slightly alkaline salt of cesium hydroxide and formic acid having the formula HCOO–Cs+. It is extremely soluble in water. An 82 wt% cesium formate solution has a density of 2.4 g/cm3 [19.9 lbm/galUS]. It has shown favorable health, safety, and environmental (HSE) characteristics in laboratory tests and has applications as a drill-in, completion, or workover fluid. Cesium formate can be mixed with less expensive potassium formate to make clear brine mixtures with a density range from 1.8 to 2.4 g/cm3. Formates have temperature stability in the range of 190 degC [375 degF], depending on the duration of exposure to such a temperature.