working gas price model vince simplified version brad model mind arbitrage condition equates trading margins across country costs transmission rise congestion network wellhead supply almost completely price elastic burner tip demand almost completely price inelastic storage rationalized perpetual call option least time variant parameters costs injecting withdrawing gas storage pipeline followed costs delivering gas wellhead pipeline intermediate variant parameters capacity dependent costs paid pipeline shrinkage transmission time variant parameters trading margins valuations storage option 8 parameters estimated major node betwork identifiable either two straightforward ways using short time series last 3 days prices based assumed variability mentioned point estimates calibrations using today data based node based model competition pipelines pipes region origination albeit markedly different terminus price versus capacity similarly competing outflows write scientific word present earliest convenience clayton