14C Quenched LSC standards are used to establish efficiency correlation curves. Efficiency correlations established with these standards are applicable to a wide variety of scintillation cocktails and quenching agents. Quenched LSC standards are supplied in sets of ten, each containing the same amount of radioactivity, but with progressively higher levels of quench. The standards are prepared in PPO/Dimethyl POPOP/toluene, argon purged and flame-sealed in borosilicate glass ampoules. The quenching agent is nitromethane. Both conventional size standards and Pico standards are available.