Tray efficiency in gas-liquid operations is a widely discussed theme, and the shortcomings of Murphree's, Hausen's, Standart's, and Holland's efficiencies are well-known. The new parameter "normalized efficiency" is defined as the ratio of the real tray mass transfer rate and theoretically maximal mass transfer rate obtained for the counter-current plug-flow model for both phases in the case of infinite contact surface. Normalized efficiency has several advantages over the previously defined efficiencies: the range of normalized efficiency is 0-1; normalized efficiency values for gas and liquid phases are equal. Furthermore, normalized efficiency can be easily used for determining the required number of trays in mass-transfer operations or for estimating the overall column efficiency. The usage of normalized efficiency does not raise any dilemma about the interpretation of experimentally obtained results for trays working in distillation and sorption columns.