Economic theory suggests that pollution tax and cap-and-trade regulations can be functionally equivalent. Environmentalists tend to prefer the firm emissions cap in cap-and-trade programs, while economists and business interests tend to prefer the price certainty of tax programs. But both may be overlooking behavioral distinctions between the two policies. Using a novel randomized case experiment, this Article tests whether the framing changes negotiated policies. It finds that negotiators reach more environmentally protective policies under the tax rather than the cap-and-trade frame, a finding which comports with real-world observations that carbon taxes tend to be higher than permit prices in carbon cap-and-trade programs. The findings have two important implications. First, negotiators treat pollution tax and cap-and-trade regulations differently—they are not psychologically equivalent. Second, contrary to the general environmentalist preference for cap and trade, taxes may generate greater environmental protection.