This article presents a numerical approach for the profit maximization by allocating an optimal injected gas in a continuous gas lift system. A performance curve of gas lift was designed that takes into account both lift and cycle efficiency. Piecewise cubic hermit interpolating polynomial is performed as a tool of interpolation to achieve a minimum error and a quantitative evaluation. A robust economic function and simulate annealing are integrated to determine the independence of decision variables and lift-gas rate, which yields a maximum profit. The model applied for a mature oil field reveals that the volume of injected gas reduces significantly by 63% and the revenue increases up to 13% compared with a conventional production optimization. The developed model will be applicable enough to enhance the profit in continuous gas life system.