Answer based on context:

There is some disagreement on which country has the largest proven gas reserves. Sources that consider that Russia has by far the largest proven reserves include the US CIA (47 600 km), the US Energy Information Administration (47 800 km), and OPEC (48 700 km). However, BP credits Russia with only 32 900 km, which would place it in second place, slightly behind Iran (33 100 to 33 800 km, depending on the source). With Gazprom, Russia is frequently the worlds largest natural gas extractor. Major proven resources (in cubic kilometers) are world 187 300 (2013), Iran 33 600 (2013), Russia 32 900 (2013), Qatar 25 100 (2013), Turkmenistan 17 500 (2013) and the United States 8500 (2013).

What are all the countries in 2013 that are major natural gas extractors?
Russia