To explore the problem of insufficient investment incentives for natural gas-fired generation in the Electricity Reliability Council of Texas (ERCOT), we use a large sample of over 134 000 fifteen-minute observations in the forty six-month period from January 1, 2011 to October 31, 2014 to estimate the effects of several fundamental drivers on the ex post payoffs of three hypothetical tolling agreements by heat rate. Our assumed heat rates reflect those of a new combined cycle gas turbine (CCGT), a new combustion turbine (CT) and an old CT. The fundamental drivers are postulated to be the natural gas price, regional loads, nuclear generation and wind generation. We find that rising natural gas prices and non-West regional loads tend to increase the agreements' ex post payoffs. However, these payoff increases were reduced by rising West regional loads, nuclear generation and wind generation. Finally, we find a substantial payoff decline due to large-scale wind generation development in Texas, lending support to the suggestion that ERCOT may transition from an energy-only market to an energy and capacity market.