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This paper discusses market power effects in ambient permit markets. A first conclusion is that the distortion observed at the manipulated market spreads to other markets. We find that the manipulated price could be lower (higher) than his competitive level according to the dominant firm acts as a monopolist (monopsonist). We show that the efficient outcome is always reached if there are as much firms as markets, irrespective of the initial endowment of permits. If there are more firms as markets, the efficient outcome is reached only if the dominant firm receipts the optimal initial allocation.