Huge discoveries of oil in the US mean that fears of global supplies running out are receding, according to the latest assessment of the International Energy Agency.

New sources of oil in Texas, North Dakota and California have put America on course to produce as much as Saudi Arabia by 2020.

New technologies mean that previously inaccessible reserves can now be reached - and old reserves kept going.

The BBC's science editor David Shukman took a helicopter flight over the vast oilfields of California.