Decarbonizing the transport sector is crucial for achieving sustainability goals, and two key strategies are the adoption of Electric Vehicles (EVs) and the expansion of Car Sharing Systems (CSS). EVs eliminate tailpipe emissions, while CSS reduces overall vehicle ownership and usage, leading to lower carbon emissions. Combining these two solutions into Electric Car Sharing Systems (ECSS) enhances their environmental and economic benefits. The integration of Vehicle-to-Grid (V2G) technology further strengthens this synergy by enabling EVs to support the energy grid, optimize charging costs, and improve system efficiency.This study investigates the integration of Vehicle-to-Grid technology within an Electric Car Sharing System to enhance Car Sharing Operator (CSO) profitability. A mathematical model is developed to optimize the financial performance of a CSO managing a station-based ECSS with EVs across five stations. The model considers vehicle driving, relocation, charging, and discharging under time-varying electricity prices. Results show that V2G increases profitability by enabling energy sales during periods of low driving demand and high electricity prices. These findings provide insights for optimizing EV-sharing systems in dynamic electricity markets and highlight the need for advanced vehicle management strategies.