Ocean sequestration of CO2 is a hopeful option to solve the global warming problems. We proposed the Gas Lift Advanced Dissolution (GLAD) System for efficient sequestration of pure CO2 at deep sea. The GLAD system is an inverse-J pipeline set in the ocean between 200 and 3000 m in depth. We have recently improved it to treat low-purity CO2 gas to reduce the cost for separation and capture of CO2 from exhausted gas. The newly developed system, named the Progressive Gas Lift Advanced Dissolution (P-GLAD) System, is to dissolve low-purity CO2 bubbles into seawater at a depth of 200-300 m and at the same time sequestrate CO2 at the deep sea of 1000-3000 m. Previous ideas of deep-sea sequestration of CO2, including storage of liquid CO2 on the deep-sea floor and direct releasing of liquid CO2 into the deep sea, necessitate the consumption of a huge amount of energy, because the realization of these ideas requires both high-purity capture of CO2 from exhausted gas and liquefaction of the CO2. To realize deep-sea sequestration of CO2 with low energy consumption and low environmental impact, we utilize a gas-lift effect to simultaneously dissolve low-purity CO2 gas into shallow seawater and transport the CO2 solution to a great depth. The present paper describes basic characteristics and performance of the P-GLAD system for low-purity CO2 gases, experimentally and numerically. It is demonstrated that the system has satisfactory ability to both dissolve CO2 gas and pump the CO2 solution. To confirm economic feasibility of the P-GLAD System, we also discuss the overall cost estimation including an additional system for CO2 capturing as well as the construction of P-GLAD. The cost for the P-GLAD is estimated to be half of those for previous ideas.