 However, BP credits Russia with only 32.9 tcm, which would place it in second place, slightly behind Iran (33.1 to 33.8 tcm, depending on the source).Due to constant announcements of shale gas "recoverable" reserves, as well as drilling in Central Asia, South America and Africa, deepwater drilling, estimates are undergoing frequent updates, mostly increasing.Since 2000, some countries, notably the US and Canada, have seen large increases in proved gas reserves due to development of shale gas, but shale gas deposits in most countries are yet to be added to reserve calculations.