Russia is increasingly wielding oil as a geopolitical tool, spreading its influence around the world and challenging the interests of the United States.

But Moscow risks running into trouble, as it lends money and makes deals in turbulent economies and shaky political climates.

The strategy faces a crucial test this week in Venezuela, a Russian ally that must come up with a billion dollars to avert defaults on its debts.

Russia has been making a flurry of loans and deals all centered on the Venezuelan oil business, money that could make the difference between the government’s collapse and its survival. In return, Moscow is getting a strategic advantage in Washington’s backyard.