Mauritania’s open, commodity-dependent economy faces mounting external pressures due to volatile international markets and concentrated trade partners. This study aims to identify the internal and external determinants of Mauritania’s foreign exchange reserves dynamics and to evaluate the country’s exposure to external monetary shocks. We employ a strictly quantitative approach using three complementary econometric models: LASSO regression for variable selection, ordinary least squares regression for assessing direct impacts, and a Vector Autoregressive (VAR) model for dynamic shock analysis. Our findings indicate that Mauritania has maintained reserves with a conservative bias – favoring highly liquid, low-risk holdings – which has helped stabilize reserves during cyclical fluctuations. However, this strategy shows limitations: reserves remain highly concentrated in a few currencies and instruments, and the system is notably sensitive to European (ECB) monetary policy shocks. These results underscore the structural risks from limited diversification and persistent vulnerability to exogenous shocks. Policy implications include diversifying reserve assets, adopting forecasting tools, and using hedging instruments to mitigate exchange rate risk.