In this paper we apply time-varying parameter (Kalman Filter) analysis to measure the degree of price convergence in North American natural gas spot markets. This statistical approach allows for an assessment of the strength of price convergence across various gas-producing basins. It is also a technique better suited than cointegration analysis because of the explicit presence of time varying parameters. Our results indicate that price convergence in natural gas spot markets has increased significantly since the price deregulation of the mid-1980s. However, results to date indicate that there is still some way to go before one can speak of a single North American market for natural gas.