What Is the Maximum Potential Gain for the Holder of a Long Synthetic Future?

The maximum potential gain for the holder of a long synthetic future is theoretically unlimited. Since the position replicates the payoff of a long futures contract, the profit increases as the underlying asset's price rises above the strike price.

As there is no upper limit to how high an asset's price can go, the potential gain from the long call component and the corresponding gain on the overall synthetic position is unlimited.