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/gal). 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 375掳F (190掳C), depending on the duration of exposure to such a temperature.