1. . 
A class of salts made from neutralization of formic acid with a metal hydroxide or oxide. Three alkali-metal formates are used in drilling, drill-in and completion fluids, (1) sodium formate, HCOO-Na+, (2) potassium formate, HCOO-K+ and (3) cesium formate, HCOO-Cs+. Clear solutions of each can reach densities of 1.32, 1.58 and 2.4 g/cm3, respectively. They are near neutral pH and meet HSE standards. Most formates can be mixed together over broad ranges of concentration or temperature without solubility or crystallization problems.