Recovery and reuse of waste energy to reduce fuel dependence on petroleum fuel, and to alleviate emissions of contaminants is becoming an important policy for managing energy and the environment. In the study, the waste tail gas emitted from the various petrochemical unit operations is recovered and reused as a replacement of natural gas (NG) to fuel furnace and boiler. On-site experimental results show that replacing natural gas (NG) by the recovered tail gas (RTG) from some petrochemical processes saves 24.6% of fuel costs and reduces 53.0% of CO2 emissions. On the other hand, if the natural gas (NG) in a mixed fuel containing both natural gas and fuel oil (NG/FO) is completely replaced by RTG, the resulting RTG/FO or RTG/NG/FO fuel mixtures saves 19.5% of fuel costs and reduce 30.0% of pollution emissions. Thus, from the viewpoint of the overall economics and sustainable energy policy, managing and recovering the energy contained in RTG assists in reducing energy consumption by raising the overall thermal efficiency. The conclusion made in this paper is expected to provide a useful technology that can be developed by industrial nations for raising energy efficiency.