More than 95 per cent of the US transport system runs on petroleum. However, car companies have been slow to develop alternatives to gas-guzzlers, despite concerns about supply and environmental damage. Likewise, energy companies are reluctant to develop alternative energies until a market is secured.

This chicken-and-egg dilemma is one of the issues raised in this entertaining documentary from wise-cracking brothers Ray and Tom Magliozzi. Their focus is on the US but the questions they raise have global relevance.