The era of inexpensive natural gas is coming to an end. That is the warning from Russian Prime Minister Vladimir Putin, who says the costs involved in developing new fields are increasing.
The Russian leader was hosting a meeting in Moscow of ministers of the world's major gas-exporting countries, which include Iran, Venezuela and Libya.
Despite the warning, Mr Putin acknowledges that gas prices - which tend to follow oil prices, with a delay of a few months - seem likely to fall in the short term.
The Moscow meeting comes amid growing concern that a new contract dispute between Ukraine and Russia's gas giant Gazprom could disrupt gas supplies to Europe this winter.
Russia's First Deputy Prime Minister, Viktor Zubkov, said on Monday that disruptions could not be ruled out as a result of the dispute, which is over the non-payment of debts.
Gazprom maintains that Ukraine's state gas company Naftogaz owes it up to $US2.4 billion, and has threatened delivery cuts if all of the debt is not cleared.
Last week, Ukraine paid Gazprom $US1 billion for gas pumped in September and October, but Gazprom wants the debts paid in full.
Ukraine - a major transit country for Russian gas exports to the European Union - currently pays $US179.50 per 1000 cubic metres of gas, but Gazprom has warned that the price could rise to $US400 from next year.