We use a large Texas database to quantify the effect of rising wind generation on the payoffs of a tolling agreement for natural-gas-fired generation of electricity. We find that while a 20% increase in wind generation may not have a statistically-significant effect, a 40% increase can reduce the agreement's average payoff by 8% to 13%. Since natural-gas-fired generation is necessary for integrating large amounts of intermittent wind energy into an electric grid, our finding contributes to the policy debate of capacity adequacy and system reliability in a restructured electricity market that will see large-scale wind-generation development. doi: 10.5547/ISSN0195-6574-EJ-Vol33-No1-8