The deal, reached between Belarussian President Alexander Lukashenko and his Venezuelan counterpart, Hugo Chavez, in Caracas on Monday, secures the delivery of up to 80,000 barrels of Venezuelan oil to Belarus every day, starting in May.

If the supplies materialize, a move that Russian experts said wouldn't make economic sense, they will cause Russian oil producers to annually reroute about 4 million tons of oil now scheduled to arrive at two Belarussian refineries. Belarus imported 21.5 million tons of oil from Russia last year, the maximum capacity of the two refineries, meaning that any Venezuelan imports would necessarily displace Russian oil.

At the current export duty of $253.6 per metric ton, Russia would collect about $1 billion per annum in budget revenues from outbound crude flows.

Lukashenko began his efforts to diversify oil imports after a spat with Russia over the New Year's holidays that revolved around lifting a discount on the oil export duty for supplies to Belarus. Russia managed to enforce a full duty — with the exception of supplies for Belarussian domestic consumption — despite being in a customs union with Belarus. The neighboring country's economy heavily depends on exports of refined Russian oil that used to be bought at a bargain. Lukashenko said Monday that Belarus and Venezuela would jointly refine the Venezuelan crude and market oil products.

Putin was scheduled to discuss energy trade with Belarussian Prime Minister Sergei Sidorsky at a session of a ministerial council in Brest near Belarus' western border. Talks were still ongoing Tuesday evening.

Russian oil companies would likely experience little trouble in marketing the 3.9 million tons that Belarus may replace with Venezuelan oil, said Svetlana Grizan, an analyst at VTB Capital. The amount represents about 1.5 percent of total Russian oil exports, she said.

The companies supplying crude to Belarus, however, such as TNK-BP and Gazprom-Neft, would not necessarily export the spare oil, she said. They may opt to refine it locally, depending on where they see higher profit, she said.

“I have no doubts about the possibility to sell this amount on other markets,” she said.

Alexei Kokin, an oil analyst at Metropol, said Venezuelan oil would be too expensive if it travels all the way to Belarus. Such a route would require the oil to be reloaded from tankers to railcars at one of the Baltic Sea ports, possibly in Lithuania. He speculated that the agreement was Lukashenko's show of defiance to Moscow in an attempt to renegotiate the export duty.

Before the talks in Belarus, Putin toured a border checkpoint, Kozlovichi-2, which will handle the customs union's commercial trucking starting in July. About 70 percent of the 4,000 trucks that cross the border eastward are bound for Russia, a Belarussian customs officer said.