A computer-implemented method for evaluating the performance of a gas lift well, the method comprising: a) injecting a tracer into an annulus (203, 216) formed between a well casing (204, 211) and a production tubing (201, 209, 210) of the gas lift well, the annulus (203, 216) including a lift gas, the gas lift well including one or more points of communication between the annulus (203, 216) and the production tubing (201, 209, 210), wherein each of the one or more points of communication corresponds to a valve position; b) measuring, over a period of time, a concentration of the tracer present in a substance retrieved from the gas lift well; c) determining one or more actual travel times of the tracer based on a deviation of the concentration of the tracer measured over the period of time from the pattern present in a baseline tracer concentration, wherein each of the one or more actual travel times of the tracer corresponds to a point of entry of one or more points of entry of the lift gas into the production tubing (201, 209, 210); d) determining one or more lift gas loss parameters, each of the one or more lift gas loss parameters corresponding to a point of entry, each of the one or more lift gas loss parameters accounting for an effect of entry of a portion of the tracer into the production tubing (201, 209, 210) at the corresponding point of entry on the actual travel time of the tracer that enters the production tubing (201, 209, 210) at each point of entry located at a depth greater than the corresponding point of entry; e) calculating a velocity of the lift gas in the annulus (203, 216) and a velocity of the lift gas in the production tubing (201, 209, 210) for each of a plurality of ranges of well depth based on the one or more lift gas loss parameters; and f) applying an injection loss factor to the calculated velocity of the lift gas in the annulus (203, 216) and the velocity of the lift gas in the production tubing (201, 209, 210) to account for a non-instantaneous velocity change, wherein the applied injection loss factor is pre-determined on the basis of at least one of: i) approximating a velocity change due to momentum; or ii) calculation of a velocity change due to momentum. a) injecting a tracer into an annulus (203, 216) formed between a well casing (204, 211) and a production tubing (201, 209, 210) of the gas lift well, the annulus (203, 216) including a lift gas, the gas lift well including one or more points of communication between the annulus (203, 216) and the production tubing (201, 209, 210), wherein each of the one or more points of communication corresponds to a valve position; b) measuring, over a period of time, a concentration of the tracer present in a substance retrieved from the gas lift well; c) determining one or more actual travel times of the tracer based on a deviation of the concentration of the tracer measured over the period of time from the pattern present in a baseline tracer concentration, wherein each of the one or more actual travel times of the tracer corresponds to a point of entry of one or more points of entry of the lift gas into the production tubing (201, 209, 210); d) determining one or more lift gas loss parameters, each of the one or more lift gas loss parameters corresponding to a point of entry, each of the one or more lift gas loss parameters accounting for an effect of entry of a portion of the tracer into the production tubing (201, 209, 210) at the corresponding point of entry on the actual travel time of the tracer that enters the production tubing (201, 209, 210) at each point of entry located at a depth greater than the corresponding point of entry; e) calculating a velocity of the lift gas in the annulus (203, 216) and a velocity of the lift gas in the production tubing (201, 209, 210) for each of a plurality of ranges of well depth based on the one or more lift gas loss parameters; and f) applying an injection loss factor to the calculated velocity of the lift gas in the annulus (203, 216) and the velocity of the lift gas in the production tubing (201, 209, 210) to account for a non-instantaneous velocity change, wherein the applied injection loss factor is pre-determined on the basis of at least one of: i) approximating a velocity change due to momentum; or ii) calculation of a velocity change due to momentum. i) approximating a velocity change due to momentum; or ii) calculation of a velocity change due to momentum.