Gulf of Ob
Gazprom's main fields are located in the Nadym-Pur-Taz region (near the Gulf of Ob) in Yamalo-Nenets Autonomous Okrug in Western Siberia. Historically, the three largest fields are Medvezhe, Urengoy and Yamburg. After more than twenty years of production, the fields are now in decline. Production from the fields has decreased by twenty to twenty-five bcm per year. The production at Zaporliarnoe, Gazprom's fourth largest field, increased until 2004, offsetting the decline in the other fields. Since 2004, Gazprom has maintained production by activating new smaller fields and by purchasing production assets from other companies.