Film-drainage models are widely used to estimate the coalescence time of drops and bubbles. These models were developed and studied based on the experimental data obtained from only a few systems. Recent studies have shown that there are many systems where the estimation based on these models is quite different from the experimental observations. The present work investigates the applicability of these models by using data from a wide variety of systems. Coalescence times of a single drop and bubble are studied at flat liquid-liquid and air-water interfaces. Systems having different physical properties are studied. All these systems contain surface-active substances. The models are compared with the experimental data. The possible reasons for deviation of these models from the experimental data are pointed out.