Bob, Rembrandt: your explanations sound coherent... anyone know when the US became a net importer? (the readily-available data series on the Web don't go back as far as 1960, let alone before). I'm going to look at the data for the UK, which recently became an importer as well.

Khebab, westexas: if it (production rate volatility) really is affected by the switchover to export, does this analysis have any interesting implications for the predictive power of ELM? Not trying to muscle in on your zetetic bailiwick, just interested.

It appears that the US became a net importer right around 1949, 21 years before we peaked. Because of a rapid increase in consumption, the US actually showed a pretty rapid collapse in net exports.