It isn't clear how hard a bargain China drove, or how much Russia might have given up, to clinch the deal. Mr. Miller said the price of gas under the deal is a commercial secret. Gazprom said that the deal included a pricing formula linked to crude oil and that it carried mutually beneficial terms.

By some accounts, China is getting a great deal. RBC Capital Markets analysts said implied terms will give China a steady supply of piped-in Russian gas at a price between 25% and 40% lower than the current cost of importing liquefied natural gas from overseas.